I think if you do the diagonal stitching to complete the grid it will be fine. I machine quilt a lot ( both long arm and domestic machine) and it sounds like you've chosen wool/polyester batting. Laundering may not make that much of a difference depending upon how much polyester is in your batting. I know exactly what you mean about not being able to even contemplate pulling out stitches: I've got one UFO to prove it!! Good luck and let us know how it works out.