Losing Fat Help? 13 Year Old?

Im 13, 5'3 and about 126 pounds. Alot of people say thats good and normal, but im on the chubby side. I dont know why though, because its mainly only my thighs and stomache that make me look fat. I know I can diet and excercise, but it doesnt seem to work. I play baseball and am still very athletic, but its just my appearance. Dieting never works because my dads rarely home so my mom gets fast food very often because she doesnt want to cook. and i really have no other choice. I usually try to get healthier fast food, like subway or chicken sandwiches instead of burgers and fries. Ive been eating yogurt for breakfast, drinking only water and skim milk, and have been cutting down on snacks like chips. But mainly its meals..excercise cant burn 60 grams of fat! please give suggestions..