I will spare you the mini-rant on men and their penises, but only because I also appreciate how men and their penises are an endless source of all kinds of amusement. Like now. ;-)
Here's a finding from a study that aggregated the results of multiple studies covering approximately 15,000 men: "For example, an erect penis of 6.3 inches is in the 95th percentile. That means that out of 100 men, only five would have a penis longer than 6.3 inches."
Feeling better?
Not quite? Well, how about this: Women's vaginas come in just as many variations as men's penises, which means while being well above average (5.16 inches, based on that same meta study) you'll be too small for some women and too big for others.
Still not enough? Okay. In that case, men report penis size is one of their top concerns. Women, surveyed about their partners (real or prospective) don't list penis size n any sort of noticeable numbers even in studies that try to capture information on physical ideals.
Nobody ever got talked out of being self conscious about a purely imaginary physical problem and that won't happen here either, no matter how much refutation you receive. So, maybe just remind yourself you're not being rational and make sure your game in terms of best positions for you and your partner is topnotch.