First time

Okay so I am 15 and last night I had sex for the first time with my boyfriend (before you start commenting judging me, it was very consensual and we both wanted to equally. I don't regret it at all) anyways, it was tricky because it was very hard to get it in bc I think I wasn't used to the size. is that normal?? every time he would get it in it would slide out. Any advice for the future or reassurance that this is normal??? 😊😊