Anal sex

My man ask me if we could have anal sex I want to do it but scared the first time I had anal sex I was 17 and it was my first time having sex ever it hurt and I accidentally shitted on my boyfriend at that time dick (embarrassing 😩) but he was like it happens 😂 now that I'm 22 and my boyfriend now wants to try it I'm scared I'm not trying to shit on this boyfriend dick cause I don't think I'll get the same reaction I got from when I was 17 how do I do this the safe way without shitting