Same thing with a small quilt my sister gave me to fix. I found matching/coordinating ribbon and used a washable glue stick. Ran the glue stick across the back. You could also use the Elmer's washable glue and just dot it to the open area. Let set a little then stitch over it. The thing is sometimes when they wash these quilts, like my ds did, they throw it in with sheets and even perma press cycle is too rough. Where the seams came open the seams were hardly 1/8" much less 1/4".