Your stitching will (should) show, because in quiltmaking, "in the ditch" means "alongside the seam." You don't actually sew ON the seam. Echo quilting is done 1/4" away from the seam and was usually done in early quilts in order to avoid having to sew through the bulky seam allowances. If you are machine quilting, you can just sew right alongside the pieced seams.