Aw! I hate that guys get so worked up over size! Think of it like this, the vagina is only about 4 inches deep!
I would rather have a guy 6 inches or less, personally. I can't stand giving oral to a really big guy because of the gag reflex, and I like rough sex, but I don't like the pain of him hitting my cervix a lot. So, in my eyes, a smaller guy is a much better partner! I can enjoy more, and so can he.
Don't ever let size bother you! If she doesn't like it, then that's her deal. Some girls do like bigger guys, but that isn't the norm! Just be comfortable with who you are! One of the biggest turn ons for girls is confidence!