While looking for a tutorial to help me make the inner reverse applique points in K-5 a little sharper [...usually can do this, but this morning.... not so much] I found an interesting youtube video on quilt as you go. I would make a couple of small changes to her method. I would sew the second side sashing by machine on the right side rather than the left - so make that double pressed piece of sashing for the back. Then I would slip stitch the back sashing rather than do machine stitching here.
you'll know what I mean if you watch the video