I've had girls be very apprehensive and tell me to take my time, or say "that's not going all the way in". Never turned down though - but it's not unreasonable at your size (over average).
She's probably only been with smaller guys. I had a girl tell me I was HUGE the other day (first time seeing my cock) and I couldn't help but laugh when thinking about the images in this gallery. I'm practically small compared to most on this site.
I dated a petite girl a couple years back (also happened to be Asian) and she didn't let me fuck her from behind and only let me use half my cock. Anything more caused her pain.