I was really nervous about butt stuff in general and my partner really helped me, and we worked our way up to it. But working up is easier than that One Thing My Partner Wants because that's a good chance it won't go quite that way and you don't want to disappoint.
I think it's worth addressing Read more… that specifically. Maybe trying for a short time without the expectation of a finish. Everything to take the pressure off.
Is that a big concern of yours? It sounds like you're happy with butt stuff in general... or do you feel uncomfortable with a strap on? Perhaps spending some time with that (and discovering that your partner really likes how it looks and gets excited by it even if you think it looks silly) might help?