I'm literally so insecure and I know I shouldn't be.

So me and my fiancé are getting married in a month, I have never had sex before and he's had sex with 3 different people before we got together. I'm so nervous about it because I'm scared he won't like it and I'm smaller than the others and he'll have something to compare me to. I know I'm just over reacting and I shouldn't be insecure but I can't help it. Do you have any advice for the first time?