How to get a flatter stomach?

I'm 14, 5'5" and 105 pounds. So I'm considered skinny. I dance so I am always wearing a leotard. I feel uncomfortable because my stomach kinda looks like a little bubble. Some of the girls have this but others are completely flat (which is what the teachers want). Sure, when I suck in, it looks fine. But just normal, I have this bubble. It makes me feel uncomfortable. I eat totally normal and am never too full but never starving. I exercise at least 2 hours a day. Also, it's not fat. There's barely any fat on my stomach. I don't understand. I don't want to feel uncomfortable and stop eating like some other ballerinas. I do ab exercises all the time. But if you could recommend certain exercises that may help, that would be great. Thanks so much and please give suggestions.