Accidental anal

So me and my boyfriend were having sex and we've had sex a couple times he's just a little under average and sometimes he slips out quite a bit anyway so he was going at it and suddenly it slipped out and rammed into my butt. I was in so much pain I was crying and I was in pain for a couple days. My boyfriend felt so horrible I kept trying to reassure him that everything was okay it wasn't his fault but he just feels so horrible. I mostly feel embarrassed because I don't really like anal and I was worried that it was dirty down there that's my main concern ironically not the fact that I was bleeding or anything. I'm just kind of scared that this might happen again and I really don't like that pain I was wondering if there's any way to kind of stop that from ever happening again?