Sounds a good set up. A good enough musician to cover up for you, and a bad enough one to show that they are inclusive.
I used to feel like that about playing at sessions, I'm not very good but it feels great when everyone's belting out a tune that I know (or even, a tune I've started)
I'll never be good enough to play on stage but being a dance caller is nerve wracking at first. I had a similar intro, a chance to call 1 dance at our club, then more, then a member with a band took me out to one of his paid gigs to do 1 dance. The first full programme for the public was horrendous, what I had prepared just was not suitable for the crowd present. With experience comes confidence and flexibility.
Go for it. Good luck