In my original blog post and in the info I passed out at the meeting, I said your "finished block" should be 12.5 inches. Just to be clear - you need to make a 12.5 inch block for the challenge. (Of course, in the quilt, it will end up being a 12" block.) Hope I didn't confuse too many of you!
I have (hopefully) updated the blog to post to say this!