Sometimes when measurements don't agree, you might find that there are 1 or 2 seam allowances that are a bit off and can be corrected easily.
Remember to press, go up and down with your iron. It is easy to distort the fabric with the "scrubbing" motion of regular ironing. Also, I have noticed that when MY DH helps with measurements, he actually pulls on the quilt, distorting it by an inch or more on a bed sized quilt. It is better to measure on a flat surface (I used the floor when I was younger.) Sometimes I "borrow" the use of a table at a local church or senior center. Sometimes I measure a portion on my dining table, place a pin then measure the rest. If I am simply trying to see if the sides agree, I fold the quilt in half each way. No measuring, I can eyeball it.