I need some help as a bottom

Hi 19M here, I have been dating this dude in my Uni for 3 months now and recently become boyfriend. I often visited his place to like hangout and stuff. But today he ask if we can crack. Now being a first time we ever do this I felt nervous but agreed. But not knowing anything I just lube up before letting him in. But I quickly back out after only tip because it hurt. He did comfort me and cuddle me but I want to know how to prepare myself properly because I don’t want to ruin his feeling.