Sometimes this happens if I use a stitch length that is too long or SA is too narrow even when I'm using a good quality quilt fabric. I get a litte careless at times. When I get s SA that I think is too narrow, I stitch a second seam right next to the first on on the seam allowance side in a very short stitch length.
I'd be upset too if a quilt came out of the dryer looking like this. I always wash a quilt using the harshest setting that I think it might encounter...like for a child, or an elderly person...to see if it'll hold up before giving it away.