How to tell my girlfriend that my penis is small

Hey! I have a problem I feel that I have an insecurity around my penis size and I don't like the feeling. My girlfriend and I started dating a while ago, so we both know how to tell her and I don't know if this is a big deal or not, and I don't want to hurt her feelings but I don't like it either. It seems like a big deal to me, and I would like to have a small penis, but that's not her thing and I don't want to put it in her face. What do I do?