I use this method for lap robes and small baby quilts.
Here's my little trick:
When sewing on the last border enlarge the stiching for about
10 inches in the middle. Press as usual. Layer and stitch all around the outside edge. Then with your seam ripper open those large stitches.
Turn thru that opening. Lay on table, use something long to push out the corners and edges. Pin as usual, Blind stitch the opening by hand then quilt as desired.
I also like to quilt about 3/4" from edge to look like a mock binding.