Eating under calorie goal

Now that I'm back at university, I can buy and eat all the food I like and avoid everything I'm not so keen on (as opposed to my mum buying everything at home).

As a result, I eat and eat but what I eat tends to be fairly low calories anyway. I don't feel like I eat "not enough", but calorie-wise some days I'm going under. Yesterday I was on 900 and looked around for something else I could eat even though I was full. I don't want to feel like I have to eat because I'm under but then I panic about "starvation mode" criticism.

But then I read the post about starvation mode being a myth and it essentially seemed to say that yes it will slow your metabolism but that's essentially about it.

So is it really that bad if I occasionally go under? Don't get me wrong, it seems like 2 days or so of the week I'll probably feel like something naughty like a pizza or chocolate and go way over my count. But most days like yesterday I'll be under.

To give you an idea, this could be a typical day:

2 poached eggs with cooked tomatoes and ham, maybe some Ryvita cracker breads to go with. (180-200)
Then if hungry again around 11.30 or so I'll have come crackers with soft cheese and ham. (150)
Then for lunch either salad (my salads with tuna and mayo come to around 250, up to 350 with extra veggies and sweetcorn) or soup with sometimes some bread or cracker breads (200 or 300)
Dinner normally chicken with green veggies and carrots and sometimes peppers. (350)
Might have an apple for a snack at some point if its a hungry day but not always (70) or strawberries with a little sweetener "sugar" after dinner (40)

So that's some days equating to 900ish, some days up to 1050. And then other days I'll have a "binge" (not really a binge though) and eat an extra couple slices of bread or potatoes with dinner or a big pizza or meal out or chocolate bar and my calories will come to 1500-1600. But apart from those days which come every 4-5 days, it's mostly around the 1000 mark.

I'm 19, 5 foot 3 and 124 lbs.

so in a nutshell, I really don't think I eat too little, but my calorie count is always under and I don't really want to eat more. I'm asking whether, for my age height and weight…is it really such a bad thing?

Also, I will probably start binge drinking once a week now that I'm back at my British university- it's just a way of uni life here when you go clubbing haha (meaning about 10 to 16 shots of vodka and mixer of tonic water or diet coke) so that adds extra calories (I never find I put on weight from alcohol much because I dance so much and don't hangover binge with food, I only put on weight if its more than once or twice per week, which it won't be).