Frankie boy, I thought that I was hiding my insecurity on this site too. But then I realised that I was revealing it to her by asking the odd question here and there scattered over weeks. Girls can smell insecurity. I have totally changed my action now. Nothing you can do about the past. All you can change is the future. And the future involves lots of lots of pleasuring your lovely girlfriends hot snatch.
Now looking back will end in 1 or 3 ways -
1) You get jealous to the point that you don't want to be with her or she doesn't want to be with you.
2) You turn into a cuckold wanting to see her with a bigger cock than yours.
3) You do what I suggest above.
I think 3 is the best option - and if 3 IS the option you may as well go with it now rather than waste time worrying
Go give her that 6 inch girth she is probably wanting.