First, measure again to be sure you got it right. It's easy to make a mistake when you are measuring anything larger than a yard or so. Also be sure you're not stretching the quilt while you measure and that it's pressed evenly. It's not terribly unusual to have an inch difference, since just 1/16 of an inch difference in each seam, spread over 16 seams, equals an inch.
Usually the part that is longer and needs to be eased in is put next to the feed dogs.