I quilted a queen size TAW a couple years ago, and stitched in the ditch on every seam. I am now a qualified expert in turning corners. Lol. The best thing I can say is; Do not try to hurry your turns. Several times I turned the fabric a few times with the needle down, to get the corner to be smooth enough to stitch. My blocks were 2.5” x 3”, with an 8” sold fabric border, so I turned lots and lots of corners.