Slow and Steady Wins the Race

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Hi there all!
Day two here for me. I did well yesterday and today in calories - BUT I am wondering how you all cope when you go over for the day in calories.
This is probably my 4th or 5th MAJOR attempt to shave pounds, but here is the deal. I usually do well in the beginning, but seem to be a perfectionist. As SOON as I don't have a perfect day, it's so easy for me to give up.
Well guess what.
Today, I went over by 300 calories. I didn't eat anything bad for me, but know that I could have made more filling choices throughout the day. But, when I got home, I was hungry, and needed something beyond what I had planned for dinner.

So my question to you all: how do you deal on a day where you see that calorie number 'IN THE RED'?

I am trying to be calm, but I want to freak out. I know I can work out, but today is my rest day, and I know I will work out tomorrow, so I am going to do my best to NOT freak out.

I don't want to burn myself out right at the beginning, and I know that slow and steady will win the race, and that it's only day two. I know it will get easier as I get into my stride, I've done it before, and have kept the weight off.

Am I crazy? Is this the way to go, or should I freak out when I am IN THE RED??