You're actually on the thin side. And since you exercise and eat normally, it's actually better than someone who's on the thin side but doesn't take care of themselves. BTW, I'm only 4'11" or 5'0", but I'm also 111 pounds :D And I also dance and run everyday (long distance runner; I run around 40 miles a week).
Oh wait, you're 12 though, so you might not have hit puberty yet. Well, that's an okay weight because you're 12 :) I'm 14 and have already hit puberty. When you hit puberty, you will gain a bit of weight, but because you exercise and eat normally, you won't be fat :)