If you are adding a final fabric border (no piecing/blocks) that may be the best time to square it up.
My thought is this, though. If it is a bed quilt, lay it on a bed, is it noticable? If it is a throw/sofa size, lay it out and look at it from a bit of a distance...
If the only way you notice this is when it is folded? You could end up making it more noticeable by trying to "fix" it :wink: