About a year ago I cut cabinet shelves out of high quality euro-ply (baltic birch). They are 21" x 21". Now that I am ready to finish/install, I see they have all developed a twist. If you lay the shelf on a flat surface and push down one corner, the opposite corner lifts off the surface by 1/4". I've had big box store plywood warp many times but not baltic birch. Is there a fix for this? Thanks.