Hey! I dated a guy who was about that size, if not smaller. It still remains HANDS DOWN the best sex of my life. Actually, a lot of my female friends and I talk about this. Sex with smaller guys really is better.
Why? Well smaller guys have to learn how to please women with something other than their penis and they have complexes about it and really try hard to be pleasing, and the truth is, this is actually preferable for women. So get the book "She comes first" by Kerner. This explains a lot about oral sex. And get practicing and talking about it with whoever will listen. Get very good at this, and no one will care at all about your penis. A lot of women can't orgasm from sex anyway, and most women can't orgasm without a little bit of clitoral stimulation. Basically, a big penis doesn't hit much of anything at all up there, unless it's too big, in which case it's really painful. The G spot is only about three or for inches in. On me, I feel like it's less than that. It can easily be reached with a finger. So there is no other part of the vagina that actually feels good, or like anything at all, during sex beyond that. If you are stimulating the clitoris and the G spot, and if you're giving a LOT of foreplay and cuddling, this will be very pleasurable for a women.
So there is nothing at all wrong with you! If you read a little about how to pleasure women with your hands and your mouth, and make sure you always ask whoever you're with a lot of questions about what they like, you really will be amazing in bed.