I've been called fat, but am I?

Okay... my cousin tells me I'm fat. People tell me not to listen to her, that she's a cheerelader, a brat, and just trying to deplete my self-worth. But some guys have said I'm fat as well. I'm 16, I'm 5'1'' and I weigh 120 lbs (give or take a couple pounds). Is that fat?? If so, I have a lot of work to do... *groans!!*