OK tthere are growers and showers, a grower can be anything small, some guy just have the head showing but when erect can be an 8 incher, and you can get a guy who has a limp p***s of say 6 1/2 but when erect its the same 8 inch, see growers and showers, and yes women love to see a good boner, but if you ever get to a natuist beach, you will see them all sizes.
so tell your g/f you are a grower, and its just nature at work, being were all differant.
Good Luck
Most girls do not care how big your penis is while limp. It is the erecton length they are concerned with. You are fine and she will be happy with what you have. If you are worry about her seeing your penis while limp, don't show it while limp. Wait till it start to get semi-erect or erect and then pull it out.