Well, I'm 13, I'm 5'1 (yeah, and I've stopped growing...) and I'm 98lbs (roughly), but I don't think anyone online can judge whether you're overweight without seeing you. You have to take into account people's muscle etc. You're only 11, and you've still got plenty of time to grow. At eleven your body can go through all sort of funny stages. I suggest that you don't panic about it. You need to forget what everyone is and just concentrate on you. If you're worried about your size, then I suggest doing some excercise. After all, there's no harm in doing any excercise, no matter how skinny or fat you are. I don't recommend that you go on any diets to lose weight. You're still only young, you just need to make sure that you eat a balanced, healthy diet.
The thing is, everyone is born a different shape and size, and when you're born with it, it's hard to change. Also, don't fret if you're a little over or under your estimated weight for your age and height. Hardly anyone will be that exact weight, most people will be a little under or a little over.
As I said, you're still only eleven, and you still have your whole life ahead of you, so don't worry about things. As long as you're eating healthily and getting enough excercise, then you're fine, and that's all that anyone can ask of you. Please don't get in a state over things, you don't want to end up anorexic. Just make sure you're doing the right tihngs to keep fit, and you'll be fine. There are many big women who do all the right things but find it extremely hard to loose weight because it's simply because it's the way they were born.