Here you can see that I was stitching-in-the-ditch on one of the corners. I am sewing in all the seams around the blocks and am very happy with how flat the quilt is laying. There are no ruffles appearing in front of the walking foot as I go along. Ruffling on the quilt top (and also pleating on the backing) is an indication that the pin basting wasn't done properly, and I used to have that happen quite regularly years ago. But now I am very careful when pin basting to make sure all the layers are taut and flat, and well pinned to prevent any shifting.
This photo shows that I have switched to the free motion foot and am already quilting the HST border. It's almost ready for the binding! I hope to have it ready to finish hand stitching the binding on Slow Stitching Sunday.