Oh, yeah, been there, done that. Now that I'm using a Sweet Sixteen, I keep asking myself every time I sit down to quilt "Where are your edges?" Quilt I'm working on now, I rolled up the extra batting/backing almost to the quilt edge and pinned it in several places, so it doesn't do that. But recently I sat down to play with a "practice" quilt I keep nearby to warm up before my project, and I did exactly the same thing that you did. Ugh!