I want to lose 30 pounds by mid/late june.

If you really want to do this you will need to plan out your meals and shop ahead of time. I shop once a week and pretty much know what I'm going to eat for every meal. It really helps you stay on track.

Some days I go well over my calorie limit. Usually it's because I need to go grocery shopping or because I am out running errands and there is nothing but fast food around... What should I do when I slip up? I messed up really bad yesterday so today I am only allowing myself about 700 calories to make up.

This is a bad, bad idea. 1200 is REALLY low for most people, especially if you're working out. Your body needs energy to function. Eat. more.

And, if you ARE tracking all of your calories correctly now, you're malnourished. Increase your intake right away.

I'm 154lb right now. I also eat a 1300ish diet but I usually eat back all my exercise calories and try not to go under 1200calories. 700 is far too low you'll be starving.

Keep tracking as its easy to drop below 1200cal in your not keeping track.

Feel free to add me as a friend.

I also recommend some weight trainings, I nearly always do some weights after my cardio.

The point to eating back your calories is to keep your metabolism up. It's not as simple as calories in vs. calories out. If you don't eat enough (and/or if you work out a lot), your body thinks you are facing lean times - it doesn't know you are trying to look good in a bathing suit. So in the short term, it does what it is programmed to do and slows your metabolism to conserve energy.

You aren't eating at a sustainable rate. You should do a little research into BMR/TDEE and go from there.

As for what you should do when you are going over - not go over? Meal plan in advance. That should eliminate a lot of the problem. Eat nutrient dense foods instead of wasting calories on processed, less nutritious calories. Find low-calorie, but filling options for days where you have higher calorie meals (vegetables are the thing to look to - I love a bowl of onion soup for dinner when I have eaten a heavy breakfast/lunch).

If you don't eat to your caloric requirements, you will seriously slow and delay your weight loss. Eventually you'll lose, but it will arduous, frustrating and non-sustainable.

I don't eat back my calories. I keep seeing people saying that everyone who exercises should d this.

Can anyone tell me why? I thought the point of exercise was to burn calories you eat? Wouldn't eating them back make exercising pointless?

Check out this example:
Abra eats 1500 cals on Saturday. << This is her gross intake.
Abra then burns 500 cals on a 2-hr bike ride.
Abra is now effectively "netting" 1000 cals that day (1500 cals eaten - 500 cals burned = 1000 net cals)

Many people start having issues when their net intake (not their gross intake) dips below a certain caloric threshold (ex: dipping below 1200 cals/day).

When this goes on for a while (i.e., being way under your daily intake goal), some people notice malnourishment side effects (ex: I started losing hair), they may have energy, cognitive, and/or performance issues, their weight loss may stall, or they really start to struggle with hunger and general diet frustration and quit.

Most people here on MFP want others to succeed, which is why they often recommend setting a more realistic intake limit (net limit, not gross limt) and encourage people to eat back at least a portion of their exercise calories to stay within a healthy daily caloric intake range. There are other methods used here on MFP where people don't eat back exercise calories, but they set their daily intake limit higher to account for regular exercise. (I use TDEE myself.) If this method interests you, search for TDEE on the MFP boards.

I hope that helps!

this is my goal as well!!!

we are almost at the same measurements! add me!!

Just make sure you are making healthy choices and fueling your body with what it needs.
You will find what works for you. What works for other people might not work for you. I was having problems not losing weight and I really had to look at what I was eating.. Sure I was under my calories for the day, but it wasn't what my body needed.

I break my workouts into three segments (now I know not everyone can do that)
But I get my body working first thing in the morning. Not much just 20 minutes I get up 20 minutes earlier than I did.
Then on my lunch ( I have an hour lunch) I got for a Curves Workout or I swim.
Then after supper and after my son goes to bed I do a group exercise with a teacher, or a home DVD.
I keep my body charged all day. I eat five small meals a day. I drink 1/2 my body weight in water (200 lbs = 100 ounces of H20) That I break up in 6 - 8 segments throughout the day.
I make sure that I have protein after my hard workouts.
I don't eat heavy after lunch. Dinner is usually my lightest meal.
I do not eat within 3 hours of bedtime. Someone told me that eat for what you are going to do in the next three hours.
And I NEVER exaggerate my time of activity. If I was at kickboxing for 60 minutes, I'll only log 50. If I am at Aqua fitness for 60 minutes, I only log 50 minutes.
You will get there!! Don't forget to measure yourself. You might not be dropping the weight on the scale, but when you measure yourself and I mean everything!! (neck, bust, chest, waist, hips, thighs, knee, calf, ankle, upper arm and lower arm) THAT is where you will start to notice. Some people will GAIN weight but drop sizes, because a pound of fat and a pound of muscle are not the same SIZE. Think of a pound of fat as a pound of butter and a pound of muscle as half a pound of butter. they are not the same size.
You will get there!! Before you know it - you will find YOUR groove, and you will be on your way!!

But yes, as someone mentioned earlier, you can do weight training - but you don't have to "lift weights" you can use your own body weight and still get strength training. Look at Jillian Michaels from Biggest Loser - she has some amazing training videos that do not use weights. She does cardio and strength training and you see the pounds fall off. Find your groove. I do not eat my calories back either. I eat around 1200 calories a day, but my BIG calorie burn days - I bump that up to 1400-1500 to fuel my body for the tasks at hand. If I don't eat enough, then I do not lose weight. You will get there... It takes a lot of time and effort and research.. You will be addicted to getting the right info!

Just to relate to your question about slipping on your eating when you're running errands, I have a snack basket in my car. It sounds terrible but I am actually really good about it. I bought 100 calorie almond packs, lara bars, snack sized beef jerkey, and natural less processed applesauce. Any of these hold me over for my twice weekly 2 hour drives or after the gym when I won't be getting to eat again for a bit and aren't going to make a huge dent in my calorie or nutrition needs.