Does doing leg weights build muscle and also burn fat?

I am a 15 year old girl and I want to lose a few pounds, my thighs and arms need to lose fat and get toned. I do weights when I go to the gym but I don't wanna end up with big muscly thighs and arms, will they look thinner and budge the fat or will they just end up massive? I don't want big arms and thighs, help!