how big should i be im 14 worried cuz my friends saw me in changing rooms and said i was small

is 10'3 cm big/small/average for a 14 year old with one testical

Not to worry about the length of your penis, but if you have only one testicle, that means you have an undescended testicle. You must have it checked by a physician. Dont put it off. If you are at puberty age, a teen, and one or both testicles is not yet descended, you are at risk for serious medical problems developing. Your doctor will fill you in on the risks. The surgery is rather routine, but very necessary.
Ricky