Wow, that was kind of hard

I just did a bit of late-night snacking and have gone over my calorie intake by about 300-400. I kind of freaked out, but then thought, oh well, I'm almost underweight anyway. I'm hoping to get over the mindset that it's okay to eat over 2000 calories and not worry about it since I've been eating 1400 for so long while burning 2200. I guess it is true that people who diet on a 500 cal deficit do get used to their lifestyle more easily XD Anyway, just wanted to rant

But yeah, how do I get a flatter stomach? Because it sticks out a lot, I exercise regularly (not crazily...just to let you know), and I do not want to lose any more weight. Is it because of my late night snacking of kashi cereal every now and then? XD

Do  you do sit-ups?

Try eating a 'cleaner' diet.... i.e. one with fewer processed foods, artificial flavourings/colourings, preservatives, sugar, salt, caffeine, alcohol and with more whole/natural/unprocessed foods, more vegetables, more water.   In otherwise slim people, fluid retention from eating too many processed foods can cause a wobbly tummy.   I've no idea what's in kashi cereals but if they contain more than 20g sugar per 100g or if the ingredients list goes past 5 or 6 items then maybe choose a less processed food.

Being underweight can also cause a protruding stomach....

I second Jane. Try cutting back on your 'artificial' intake. I think too much caffiene and too many sweeteners are both bad ones particularly when it comes to keeping a flat/not-bloated stomach. Increasing one's calories can also cause a temporary bloat while your body adjusts. Mine was terrible, once, but it has now calmed down now my body had adapted. In time for college, too!

And good on you for eating more and not sweating it! Everyone eats more than usual sometimes, it's not abnormal. :D