I would block the panel first, using lots of starch to keep it in place. Once layered, I would also do a *lot* of quilting to ensure that the fabric is stabilized to the batting. Batting is more stable than fabric (at least in terms of skewing), so permanently "glueing" the fabric to batting with quilting stitches is the best way to ensure that the quilt lies flat. If there isn't enough quilting, the panel will try to distort back to how it came off the manufacturer's rollers and will pull the batting along with it.