How can I keep the weight off?

I hurt my knee and I can't do athletics or run or do any exercise until it heals. So, what should I eat and how much should I eat to keep off the weight and hopefully even lose some. I'm a 13 year old girl, I'm 67 inches tall, and I weigh 117. I'd like to weigh 105ish. I know that's super skinny but I need to lose some weight to play basketball more effectively. Thanks for all your help and I will add on if anyone has any questions.