Trying Anal Issues

Opposite of what seems to be the normal situation, I want to try anal but my boyfriend is not that into it. I talked to him about it one day and he said if I really wanted to then he would try it. He started with just his fingers, and the feeling was strange but good. After only a minute or so though, I had the feeling that I needed to poop. I told him to stop because I didn't want it to go bad the first time trying. Is this a normal feeling that comes with anal play? Does it actually mean you're going to or is it just how it feels? How do I prevent that? I want to experiment more but don't want anything to make it a bad experience especially since it's me pushing it and not him.