Most Helpful Guy
Certainly not! C cup is medium, so you're just fine. A 12 year old boy may well be just teasing or may well be just plain nasty.
For what it's worth, I openly state here I prefer A or B as being small boobs. Also, my sister is 32A at best and is very happy with what she's got.
Most Helpful Girl
Ok, first of all, I don't think any sane person would tell you getting breast implants at 16 is a good idea. You're only 13. Your breasts haven't stopped developing yet and probably won't for another couple years. Also, c cup is not flat chested, or even close.