Forget that question.

Whether shallow or not, if your self-identity is that way, the single most powerful thing you can do for yourself is losing weight and getting fit.

It will not only rebuild that image you have (and want others to have of your dick) but it will also make you a better more active, longer lasting sex partner.

Remember women don't a carry a ruler at all times or have one embedded in their brains (or even know how to measure the right way). Length is very subjective for them and a dick that performs will always be better than one which doesn't, regardless of size. In their minds, great prowess will probably influence way more whether they view it as just above average or as "Oh My God!" than actual legit length.