Good for you for practicing safer sex. See our answer to Is Anal Sex Safe for some of the risks of anal sex and how to keep yourself protected from STDs.
TeenHealthFX does not think there is anything wrong with you - if you have anal sex, it is almost inevitable that feces may end up on the penis or condom. To minimize the chances of feces getting on the condom you can clean around the anus before sex with a wet clean cloth. It is better not to have a bowel movement just before having sex. The penetration of penis is unlikely to go up to the internal sphincter (where the feces are), so that will prevent the feces from getting onto the condom.