Use your shyness to propel you to do your best. You don't want to make a fool of yourself, right? So use that fear as a motivating factor.

Also, you might try the total stranger approach - my first song circle experience was on vacation, thousands of miles from home, among people whom I'll probably never see again - though I wish I could, it turned out so well. I went home and organized a song circle locally - again, the in first meeting everyone was a total stranger to me. If I'd wanted to quit then, I could have. But it turned out so well I've kept it going on and off for three years.