Have you considered doing diagonal crosshatching instead? You can still use your walking foot, but there wouldn't be so many turns and it's easier than staying in the ditch. Start at one of the corners and stitch all the way to the other corner. I've seen diagrams of how to do this with the minimum of starts and stops, but I think your main concern would be stabilizing the quilt well before you start. This is what I mean -
http://www.allpeoplequilt.com/videos...e-quilting.htm
Edited to add - I meant to tell you how beautiful your quilt top is. I think that's a wonderful design and beautiful colors.