Doing a dry fit here and am not sure how to square this. I've seen alot of videos on how to check for square with a diagonal measure but not what to do if it's out of square. There will be a back which is not yet cut so I will have access to just one side. I'm assuming angle the clamps in some way? The bottom is square but the top is not. This is a non shop piece or it would be close enough, lol. Thanks.