I'm worried I'll be bad at sex....

I'm 20, and I just started dating a guy I really really like. We haven't had sex yet, and I found out he is really, like really well endowed while making out with him, and now I'm really scared how I'll be able to handle that. I've had sex with about four guys before, and my cervical length is so short that it always ended up me being in a lot of pain and not being able to do a lot of fun stuff. Also I have massive gag reflex and that kinda was a problem previously.

I really like him and now worried that we won't have fun and I'll end up disappointing him. What do I doooooo? 😩