hey! well, what I've heard helps, is to run/jog in the mornings, or whenever you can get it in, but I think its best int he mornings, though I can't tell you why :) because I'm not sure.
also, definitely sit ups. It may take a little while, but the more you do the better. That will help you get a flatter stomach and eventually if you continue doing them ( as many as you can before bed or something) then you could get the ol' abbs :P
anyway, I'm trying to flatten my stomach too, and that's what I aim to do. Sit ups :) so good luck! :)
oh, one more thing. I know it isn't my place to tell you this, but I'm going to anyway. If a guy doesn't like you because of a little fat, he's a waste of your time :D not saying that working to flatten your stomach is a bad thing, I just hope no one's forcing you to... :]