After pinning almost the whole sandwich, and then realizing that the backing wasn't quite straight, so didn't reach the edges, then unpinning, I realized it would be much easier to just tie this quilt. The "batting" is the backing so I don't have to worry about the layers shifting. I'm tying about every 3 inches and I think that will be enough. I'm using 3 strands of embroidery floss for the ties. I think it will work OK. When I'm done I'll just sew around the outside then put some binding on and call it good. It doesn't take too terribly long to do the tying, and I found an explanation of how to do continuous ties so I don't have to stitch-cut-tie every single one. I can stitch-tie-stitch-tie etc, then cut. It goes faster and it's easier to do the tying with shorter strands so I don't have to waste so much floss.