Too tight? (Tmi)

My boyfriend and I tried having sex for the first time today (with a condom) and we couldn't get his penis inside me ? I was nervous because I've never had sex before but he has and after trying for a few minutes he went soft and we stopped and went back to oral. I'm not sure why we can't get it in but probably because he's pretty big. I use tampons on a regular and when I masturbate I can get 2 fingers up there so I don't know what we're doing wrong. Any tips or help would be great.