suggest you use your feed dog foot and stitch in the ditch. I cant FMQ to save my life I use this foot all the time even when I am tracing around part of a bear. (I make mostly kids quilts I do not have the room to make any bigger one)
I know this does not help you much on this project (sorry)
OK I looked at the PB and suggest you quilt. around the centers. then around the sashing. depending on the batting you are using you should quilt no more than 3 to 4 inches apart. then around the borders.