"If I'm going to practice, practice, practice, it will be on something I actually enjoy."

...and yet it sounds as though you enjoyed performing a tune you'd never seen before (Prospect from Southern Harmony), and you enjoyed the praise you received afterward. My humble opinion is that if you grit your teeth and devote the time to improving your skills on the guitar and discovering what the instrument has to offer you, you WILL have more enjoyment with it in the long run. Put in the time; it will be worth it.

But for short-term results that are required for an upcoming service within the week, I suggest a compromise with your choir: tune your guitar up a HALF-step and have the choir sing a half-step lower.

More thoughts:

Why not accompany the choir using an instrument that you enjoy?

Why not recruit other musicians in the congregation to help you out? (If you are playing flute, let's say, and someone else is playing clarinet and a third is picking out single notes on a piano, you have a three-tone accompaniment.) Jeez, are there no families in your congregation who have kids who play in the school band?

Others here have entreated you to quit your bellyaching and open your mind, but you seem unwilling to budge. Here's a URL of an article on what the Bible has to say about stubbornness: http://www.ehow.com/about_4587766_what-does-bible-say-stubbornness.html

:-)

Sharon