Do i need to loose weight?

Im 13 i weigh 11 stone and i am my height is 5'8 i eat sensibly i don't really like sweet foods or pastries because they make me have heartburn so i eat salads and fruit i am at the gym a lot and i am in a lot of sports i rarely eat chips or pizzas but 3 weeks ago in school my cl were doing something in science that made us weigh or self's and my weight has never been a problem but the girls in my cl said for being 13 im fat since then i feel self conscious i don't know what to do ami fat?