I dont *think* im fat but im really big?

im a girl 13 5'8, 170.. humongous, right? But my fat percentage is 17%. I know thats kinda alot but i think i should weigh less. Im just soo big!! i cant stand it i want to cut my legs off or something...... why is it like thiss??? is there any way to loos body mass? I cheer so i cant lose all my muscle