If you're doing cheerleading, dancing, swimming, netball and walking, you'd have to be eating an awful lot to be overweight.  Today, many girls think stick thin is the way to be.  It's not.  At 11 perhaps you're starting to develop the women's curves and breasts.  That's great.  And it's not fat - it's shapely.  When you really wonder, take a look on the internet for the most recent America's Next Top Model.  She's what you should want to look like - and believe me she is beautiful without being stick thin.  And remember, if you should ever be teased about your weight and you are this active, it's probably that someone else is jealous because they haven't yet developed like you have.  (Keep an eye on the boys and who they look at - no doubt it's you and not them.)