Am I fat? Or muscular?

I am 13 years old. I am 5 foot 8 and weigh about 158 pounds. I work out regularly in athletics such as cross country, track, and softball. I ask my friends but they say i am pretty muscular? But would muscle really weigh this much? I know I have a little flab? Should I workout more and go on a diet? Am i fine? Is it really muscle or fat?