How do i get a flat stomach???

im a girl, 12 years old, and about 111 pounds. im very active and have alot of muscle. i am playing softball on an all-star team right now and our coach makes us run alot like we run the bases a lot and stuff and run around the feild for warm ups. i do cheerleading in the summer (starting in august) 4 nights a week for about 2 hours. and take ice skating lessons during the winter. i drink alot of water thats basically all i drink except for an occasional soda or juice. i use to eat alot but i never agin a ton of weight i will gain like a pound or 2 and since last year i only gained about 3 pounds. some of the things i eat or what i eat like is....chips and dip....granola bars....ice cream....strawberries.....(fruit in general).....cereal and other stuff im not fat and a lot of my friends say that they wish they looked like me. but how can i get a flat stomach by summer and thin out my legs/thighs? i also eat less than i use to :)