Are my legs getting fat or muscular?

see im 15 weigh 89lbs im 4'10 1/2 and my period just ended june 21st i dont know if im still retaining water but my inner thighs seems bigger, my inner thigh measures at 19 and my lower leg measures at 13 is that fat or skinny? My inner thigh does not jiggle if i try to make it jiggle it doesnt but feels heavy what is that?