15-year-old girl, 5'2", 102-106 lbs... am I fat?

You are NOT fat, you are probably actually underweight. You need to eat more, everyone is supposed ot get at least 2000 calories a day, more if they exercise. Yes, you are short, but i'd be willing to bet that you're still growing, and once you get taller, if you do have a little bit of body fat, it will thin out. If you can see your ribs and hip bones, it's unhealthy.