Honestly, don't worry about it. And I really mean that. If you obsess over it the more it will become a problem.
This is not a physiological issue. You are average, in regards to your erect length. It is a psychological issue for you. The more you feel inadequate the more you actually will be inadequate in bed. The more comfortable and confident you feel about your penis, the more comfortable and confident you will be in bed. Women will always prefer confident lovers over inadequate ones. Thus, your feelings about your own penis will impact your sex life much more than how women perceive the size of your penis. It is much more likely for a woman to have a problem with a man because of his own perception of his penis rather than her own perception of his penis. Got it?
Trust me, you can definitely please your lovers with what you have. I had a teammate in college who had less than you in length and he did quite well for himself. In fact, he did much better than the rest of us, numbers wise. And many of those women came back for more again and again, sometimes two at a time.
Lastly, for many, if not most, women, sex is more psychological than it is for us guys. If she is genuinely attracted to you as a man, and even more so the more affection she has for you, the easier it will be to please her sexually (and the more powerful her pleasure will be).
My advice is this, be confident, but focus on her. Pay attention to what she likes, and communicate with her. Make sure you know what she likes. A man who tells a woman how much he cares for her and how much she turns him on, pays attention to her sexual needs, and is confident about himself, is MUCH more desirable for women than having a large penis.