^ Stop hating your body. Easier said than done, but as someone who used to have every insecurity known to man, I can say from experience that when you hate your body, you tell yourself things like: "If I just lose 5 more pounds I'll be happy." And then you lose 5 more pounds. And you're not happy. And then you say really crazy things like: "If I just lose 5 more pounds I'll be happy!" And then you lose 5 more pounds. And you're not happy. And then you say completely stupid things like: "If I just lose 5 more pounds I'll be happy!!!
Have you seen the movie Mean Girls? There's a scene in it where they're all standing in front of the mirror looking for things about their bodies to complain about. When you're insecure about your body, or outright hate your body, it doesn't matter what you look like, you'll find something to complain about. Right now, I'm not overweight but I am overfat. That's an objective fact. But I've never felt more confident with my body image. Back when I was in high school, I had the lean "Fight Club" look all the teen boys are crazy about having, and repeatedly got "Wow!" type responses when people caught a glimpse of my muscles. And at that same time I had horrible body image issues. I thought I wasn't muscular enough, I wasn't ripped enough, etc etc. I probably looked the best I have in my entire life, and yet I felt the worst about my looks. I don't want anyone to go through that. Exercise out of love for yourself, because it's good for you, because it'll improve your bone density and musculoskeletal health and coordination and cardiorespiratory function and hormones (I hear 13 year old girls have those). Eat healthily because it's good for you. Don't punish yourself for not looking a certain way, but reward your body for being yours by nurturing it with what you put into it and what you do with it.