Losing virginity

My girlfriend and I tried having sex for the first time but when I tried to put my penis into her it wouldn’t go in. The tip was pressing up against her opening but it just wouldn’t slip inside. My girlfriend said she felt a little bit stretching/pressure down there so maybe a tiny bit of my penis went in (if it did, it must of been like a tiny bit of my tip and that’s it).

She’s was very wet and said she felt ready for me to be inside. We did around 40 minutes of foreplay. I had a condom on (if that’s relevant?) so does that make it more difficult to enter on first time? We also only tried missionary positions.
Advice? What can I/we do to make sure next time I’m able to get inside?

All suggestions welcome.