You are boring and that's okay. Not being open minded, not being kinky, being too reserved and uptight or a clean freak are not crimes. You haven't done anything wrong.
You have 3 options:
1. Suck it up and learn to try new things, it's not like she isn't going to take a shower before making you eat ass. If you hate it after trying it that's a whole nother thing.
2. Show her that You're not a boyscout but that you have certain limits by making up for it with other things. She won't mind if you won't do one thing if you do plenty of other fun things she'll love. (For example, I know girls that won't do anal but would do a threesome with another girl or vice versa. Girls who won't send nudes but would give me a lap dance/twerk for me, girls who are too insecure to wear mini skirts or booty shorts but would buy lingerie for us to enjoy at home, etc.)
3. Just let her know that you're a missionary with the lights off in a bedroom only kind of person and she has to accept that, if she wants something less vanilla she can go on Pornhub or buy a toy.
I recommend 1&2.