First time...

My boyfriend and I tried anal for the first time about two days. I would like to first say that for the longest time I thought that butt stuff was weird. I'm a stick to my comfort zone kind of gal, but I'm open to try something at least once. Anyway, a few weeks ago my boyfriend said that he wanted to try something new and so I gave him the green light. The past couple of weeks while we're having sex he would gently glide his finger in with some ube. Honestly, at first I was uncomfortable, but then it started to feel good, like really good. So a couple days ago we were having some really intense sex and well I was in the doggy style position and he decided to lube up and give it a go. It is definitely a different feeling. It kind of hurt a little bit , but he was being super gentle and going really slow. I was super turned on, but I just couldn't handle it. I was terrified of pooping! We tried a different position but again it just felt like it was too much. I feel like I might have ruined it for him or disappointed him because I couldn't handle it. He says that it's okay but I feel like he's lying to make me feel better. I would love to give it another go, but that feeling of needing to go number 2 is just so uncomfortable. Is there anything I can do to make that feeling go away or less intense?