I also usually add this on to the last dance of the evening. Call for everyone to promenade into one big circle, then tell them to join hands and circle left. That's your last call for a few minutes. (You will want to warn the band before the last dance that they will be playing for longer than usual!) Join the circle, drop your left hand, and start spiraling in. Turn back over your left shoulder and spiral out again, passing face to face with everyone else in the line. Lead the line out to a big circle, join the line into a circle again, and (three minutes after you called "circle left") you call, "And back to the right!"

I could tell you a few more variations that can be done of this, but you have already gotten lots of good advice about how to do it. It sounds like you need reassurance that you can do it. You can. Just remember that the point is for everyone to see each other and enjoy being together, and you'll do fine.

Jacob