It doesn't fit.

I don't think my penis has a big diameter but my girlfriend thinks it does. It just doesn't go inside her vegina. Also, I have difficulty locating the cavity. The other day I could see that it did go inside of her a little bit. She said that she was the one who did not let it to go in any further and probably made it too tight. She wants me to go in all the way but on one hand it does go and she tells me to rub the opening a little bit so it opens up and I get tired and my penis becomes soft. On the other hand seems to control the opening. Please help. What to do?

Hubby had same issue.

Don't worry, she will be able to take you in soon. My husband's penis is large with a very large girth, and when we first started it was really tough. With adequate lubrication and foreplay, and practice, it will be able to slide all the way in your girlfriend and you will both be very satisfied. I know how she feels - I was excited yet terrified when I first saw my husband's massive member! I used to be a sex therapist before the children came, so here is something my husband and I tried. Allow your girlfriend to stroke your phallus and coat it in lubricant as you insert your fingers into her vaginal opening and pump. You will become extra firm as she pumps and squeezes her fingers around your penis, and she will begin to loosen up and get wet! Then, ease in starting at the tip inch by inch - it is very erotic and sensual if you go slow - allowing her to guide your penis with her fingers. If you feel yourself go limp inside of her, sometimes my husband sticks a finger up in my alongside his shaft, stimulating himself into a bigger erection and keeping me moist. Try it! It might be difficult at first for your girlfriend to accommodate both your large shaft and a finger or two, but she will grow and stretch as you do it more often. Best of luck to you!

Of course it fits!!...

sounds like a little Lubricant would go a long way Good luck sit dat!