Squaring up a show quilt is way different than for a bed quilt. My friend who does show quilts measures and remeasures everything as she makes the quilt making sure everything is squared up, then when it is all together including binding and hanging sleeve, she will pin the quilt to a base like a large piece of cardboard or maybe even the carpeting, measure the sides and make sure the right angles are right angles, then she will steam it, blocking it. That is a lot or work for a bed quilt. I just try and measure and stitch everything correctly, then I load it onto my long arm, I have learned that if I can, I use the selvage edges of my backing to both trim the backing, so the sides are even and to attach the backing to the leaders. I then do the quilting aiming to keep the sides of the quilt straight, so I don't end up with one end of the quilt narrower than the other. I then take my quilt off the longarm and move it to my six-foot cutting table and use my ruler to trim the edges making sure I have kept everything straight and all four corners square. And like Tartan, when I fold the quilted top, I check and make sure it folds up square.