This is going to be another one of those "is my penis too small" topics

, but I really am worried. My brother showed me this forum, so I think it is a good place to ask questions. Also all of those other websites with 13 year olds talking about their 9 inch long penises aren't very encouraging, as fictatious as they may be.
Firstly, I am fifteen years old, taller than most people my age, and I'm begining to grow some hair on my face (very short and sparse though). I also have a helluva armpit hair, which might mean something. My flaccid penis length is about 2 inches or about 6 cm long (though sometimes it is slightly longer). When I have an erection, it is about 9-11 cm long (personally I don't carry a ruler around, but I compare it with other body parts like the length of my index finger and the space between the thumb). Basically my erection is about 4 inches long.
So please tell me if this is too small for my age or not, I am a somewhat concerned individual.
Thanks