Getting Down

So my boyfriend and I just recently had sex for the first time. We were doing great until it was time for him to go in. For some reason he wasn’t fitting, so I tried relaxing but it still wouldn’t go in. We tried like 4 or 5 more times, then just gave up after that and did other activities. I’m just concerned as to why he wouldn’t fit. He’s average size and was very hard. Is it something wrong with me? Am I too small?

I would love some help with this, thank you so much.