gillyo

I make wall quilts and always sew a line of buttons on the back of the bottom edge. The extra weight
keeps it flush to the wall and as long I make sure it's square it hangs beautifully. For competition quilts I blanket stitch seed beads onto the bottom raw edge before sewing on the binding. You can't see or feel them and the added weight helps it to hang straight.
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Those who make show quilts construct them differently so they'll hang straight. There are a lot of tailoring techniques you can use to make that happen. The fact is that "big time" quilters are highly skilled and have their secrets, I guess that's why they win the big prizes.