5" girth is only about average, so you shouldn't have too much trouble with intercourse. Girth rather than length is the problem for penetration. Many women are apprehensive that their first time will hurt, which means they get tense which means that it hurts. You have to do all the right things like we all do and hug her and caress her and get her relaxed and bring her to orgasm before penetration. But at the end of the day it's probably going to hurt her, and you have a choice to either do it or not do it. With my now wife I did it and it hurt her.
Later, next morning in fact, sex was much better for her and for me. But that first time was not pleasant, but this is the way it often is.