The prostate is a walnut-sized gland located between the bladder and the penis, just in front of the rectum. This gland is not visible from the outside. I believe you may be referring to your testicles, also called testes or balls, which are oval organs that lie in the sac (scrotum) that hangs behind the penis.
The testicles of normal adult male can range from 1.5 to 2.75 inches. It is best to discuss your concerns with your doctor.
For more information about the male anatomy: http://teens.webmd.com/boys/default.htm