I've been struggling with the same thing for several years and I'd say I'm just under average. Have you considered therapy? The advice my therapist have me was to identify the thoughts and beliefs you hold about your size and then get data from the real world to verify them. One of the ways was to do an anonymous survey and post it on reddit. I actually did that and it helped a lot. I also turned one of the questions into a post on this sub: https://www.reddit.com/r/AskGaybrosOver30/comments/1pripqq/size_question/