Everyone has fat. You can never get rid of it all. If you do you're at risk of dying.

You can work out all you want, if you don't watch what you eat you'll never have that "chiseled" body.

Are you a guy or a girl? Because if the ladder, I would expect you to have a bit of fat on your chest, if the former then I'm wondering why you're worrying about your butt.

Seriously, go outside and have fun and play. You shouldn't be worried about a small amount of fat at your age. You're not even through puberty completely. Your body is going to be changing a heck of a lot over the next few years.