mornin Kimmy, First of all, one has to like anal sex to begin with as it's an acquired taste. I myself don't like it but every now and then i will let my husband poke me in the pooper. He likes it but it's not something he wants all the time, just once in a while for a change.
It is your absolute right to not like anal sex. If your uncomfortable then you must tell him that your not down with it. If you feel like you can accomodate his desire to do it once in a while, that's ok too. What helps me are a few cocktails lol. It seems to relax me and we do get a little uninhibated when we have a few nips. Also you must be plenty lubed. We don't produce our own natural lubrication out of our butts like our vagina's, so a lot of KY or Astro Glide is 100% needed. And you should be really, really turned on first. If your totally hot and ready, then it works better and it does feel pretty good once it's in there.
You did not let your fiance down at all. He loves you and wants you to feel good too. So just let him know that anal sex is not really one of your specialties and you really prefer it if he doesn't ask for it. But like i said, every once in a while, if you can, is ok.
:-) x