This should really be in the sexual forum.
Penis size really is not a factor in this, its technique, I would suggest a good book (but cant think of one so I am really no use to you lol).
Or a good web site, something to give you both ideas on what you might or not might to try ?
I have had several lovers with various size penises and I swear its nothing to do with it.
You need to talk to your partner about this. I am sure someone will come up with a good book/web site for you both to look at.
Even with a handicap making love can be fantastic.