Your measurements put you at just a little over average. Which means your penis is larger than at least 50% of males. You cannot permanently increase the size of your penis. There are options to increase the size temporarily, but nothing is permanent. (If a company ever discovered a product that could, they would be squillionaires I swear! lol) So many males worry about this, but you can't change it, so it is fruitless agonising over. Even surgery doesn't actually increase the penis length. They simply sever the tendons (or whatever) that hold some of your penis inside the body, so it hangs out more and looks bigger when flaccid, but it is still the same size when erect as far as I remember reading.
Anyway, I agree with others. Size is not important for being a good lover. Many younger men tend to believe that the most important aspect to good sex revolves around their penis and penetration. This becomes their focus: "I must be bigger and girthier and last longer and longer and fuck harder and quicker" They do this believing this is what women ultimately crave and desire above all else...possible because it is the main focus in porn, or that so many people believe or perpetuate the myth that penis in vagina penetration is the end goal, the ultimate experience, the one true way.
Penis in vagina sex is just one sex act among many. have you considered that having a 6 inch penis will help women to be able to take more of you in their mouth, or that she might find anal sex more comfortable? Have you considered that many women cannot orgasm from penetration alone and therefore would not rate it as high up their "orgasm scale" as oral sex, or being touched? Yeah we love penetration. It feels great because it stimulates the g-spot (Which is only like, 3 inches deep...easy enough for a 6 inch penis to reach).
I don't know about other women, but I suspect this might be true for lots: It is not just physical stimulation we get from sex. A lot of the thrill is mental (feeling connected to our lover, getting turned on listening to his sex sounds, the idea that he is inside us...etc) I would say its 50/50 physical and mental for me and it doesn't matter what size penis he has, the mental thrills are still exactly the same.
I know, as a human, with a body that contains some parts I wish looked differently, that it is very hard to just stop worrying that you "look wrong" in some way. Most of us have this. We are all our own worst critics. However, you need to know that no one is perfect and I can tell you this....when in bed with a woman, she is most likely to be worrying about her own perceived flaws than to be focusing and scrutinising yours. She most likely wouldn't even notice and if she did, she wouldn't care because she actually quite fancies you (or she wouldnt be in your bed)...and if she did care, shes not worth it anyway! (Be with someone who is not so shallow as to critique your normal, human, flawed body) When I slept with my guy for the first time, I cared about him. Love and lust is a funny thing....it makes us overlook and only see the beauty in our partners. Their flaws often become our favourite things because they need more love! lol