First, get some information. Average male penis is 5.5 inches when erect. Research shows that most women don't care what size a guy is, as long as he is able to use his erection effectively when engaged in intercourse. Most women cannot orgasm vaginally, or usually do not orgasm vaginally. Why this is good news for guys is because learning what women in general like, and what the woman you are with specifically likes, is all that it takes to be better than average in bed. Most women are satisfied to have an orgasm before penetration, either manually or orally, and find your penetration the icing on the cake, no pun intended. If you are merely masturbating, then who cares what size you are except you?
Stop obsessing about your size. Find a women you are into, win her over by your personality and discover what makes her feel good sexually. Take your time with this, and if it doesn't work with her, find another. Wash, rinse, and repeat. Us men make this way more complicated than it needs to be. I was like you in my teens and early 20s. It wasn't until I did some research that I found out I was above the average and that I was normal. In those days I had to research Masters and Johnson's studies, today the internet gives you a lot more information.
Lot of younger guys posting of late here about their size. The age of internet porn is really messing with a lot of you younger guys, and I feel badly for you. You run the risk of wasting your prime sexual years worrying if you measure up to an unrealistic ideal. Don't do that. Having a big penis won't make you feel like a man as much as sexually satisfying a women you're crazy about over and over.
Put your penis down and get in the game.