My cock is big though.. it might reach quite far If you stick your finger up your ass you get shit, just like if you stick your finger up your nose (even after blowing it), you get mucus. Welcome to the real world
Relax and enjoy it. If there's a bit of poo around just give it a wash after. As long as you are not suffering from stomach ache or the runs, then there's little chance of infection. Worrying about stuff makes the experience less pleasant. Have fun.
I like watching anal sex in porn but the thought of the mess in reality grosses me out. It is not so bad doing yourself with a dildo but someone else seeing any accidents..ick. Also, sometimes I find it hard to enjoy anal, it feels like I need to go to the toilet