I don't like stitch in the ditch - you can't see the stitching and it is often hard to do because of going thru multiple layers. Without seeing the pattern, my first inclination is just put an X thru each block ~ lots of straight lines and you can mark them w/ masking tape. Easy Peasy.
I don't get the purpose of the press & seal??? I just use frixion pen or pencil. It doesn't come off, even w/ the rubbing of my hand over the quilt w/ the hand quilting.