Originally Posted by GingerK

If there are any seams that are REALLY off, I would open and resew. Otherwise, it may be a case of the various fabrics having stretched a tad here and there. I have had luck in laying out my block and 'blocking' it just like you would with a sweater. Lay it on a flat surface and pin/tape it into the size that you want. It may mean trying to stretch some areas and ease others. Stretching can be made easier by very slightly dampening the cloth. Once it is the size you want, wet it down with a spray bottle and then let it dry. This also works for panels that are skewed.