Thanks Barb and Iceblossom for the suggestion to do a stay stitch. I'm assuming you both mean do the stitch on the quilt top (before putting on the longarm for quilting). I've never done a facing, but most of the videos I've watched also do another stay stitch (top stitch inside the seam allowance) after stitching the facing to the front and pressing it away from the seam.
(And doing it before will also give me a nice line to follow when basting the top on the longarm.)