Thank you all for all responses and so sorry about replying late. The only worrying is because I only had sex with one woman, my gf, and she only had sex with me too. But one of the things that is really freaking me out is, if I have sex with another girl whose had sex with other guys, if my cock is going to be "a problem"... maybe she only had sex with big cocked guys and she "laughs at me" or she makes me embarrased or... I'm really insecure about that topic. I posted pictures of me in the Male section a while ago (now deleted) and not many girls really commented. And is not about comparing me with porn actors with cocks as big as the Empire State...
Thanks for the answers, you are really nice people