Piano Dread

I first took piano in first grade from my mother and then went on to take from Mrs. Keeler, a thin, astringent woman with a whiny voice, who scolded me every week because I had such long fingers and therefore such potential, and I was throwing it all away by not practicing. Tired of the scolding and the obligation, I wheedled my mother long enough that she finally let me quit. I think I convinced her that I wanted to be a student instead. (not that it had to be an either or). Anyway, it was fourth grade and John Thompson's Book Four that I ended with, so of course, my piano abilities have always been very limited.
Still, periodically over the years I have had to step in to pinch hit on the piano. When we arrived at the Aspen Ward in Colorado one Sunday, they nabbed me, figuring I knew how to play, and I was stuck because they had nobody else. Then once I had the calling to be the Primary pianist, this when we had no piano at home to practice the tunes on before the meeting. Now, we live in a ward where nobody seems to play the piano. It is a Mormon phenomenon, because I thought that every ward had a fair share of decent pianists. Suddenly I found myself as the Relief Society pianist, stumbling a bit every week, but amazingly getting stronger as I went. Now I can sight read most hymns and manage them after a couple of times through. (Thank heavens for the prelude where I get to practice and all the sisters are chatting in Relief Society.)
But now my goose is cooked because I have to accompany a quartet on Sunday for Mother's Day as they sing "Home Can Be a Heaven on Earth" in a new and more difficult arrangement. My heart stops when I have to play the piano in front of anybody and on Sunday, I will have to play in front of the entire congretation. What have I gotten myself into?