how do i get rid of annoying belly fat?

i am active but everytime i eat my stomage grows! i mean i am 80-85 pounds (im 12) but i look REALLY fat in a tank top or a shirt that hugs me! i mean i cant were ALOT of my areopostale shurts cause they make me look fat! i want to loose that belly fat without loosing to much weight! also i am vry small so thats why i weigh less