Hi. Do not be worried. You are good. I am 19 years old and 7 inches but as you might have heard over and over again...it is not the size but how you use it. The average penis size Like Ryan Mentioned is 5-5 1/2 inches. To prove this to yourself, next time you're having sex, go CRAZY. Go fast and deep and think of other things so you do not have your orgasm too fast. You'll see how much your partner enjoys the ride ;)
I believe the normal size is about 5 - 5 1/2 inches. You are fine. Plus most women dont even care about size, they care about a whole bunch of other relationship-type stuff.