Never accept the yardage listed in a pattern as gospel. It's quite simple to figure yardage for your backing. Measure the width of your top, divide it by 40 (width of 44 inch fabric less selvage and shrinkage). That will give you the number of widths for your backing. (This may be larger than you need, but you can trim. Extra fabric can be used for binding or go into your stash.) Then, measure the length of your top. I add 6 inches to allow for any shrinkage due to the quilting. That will give you the length of each width. Then you sew the three panels together. If you need to trim, cut or tear off excess from two outer panels. I also leave 3 extra inches to each side as well as the length. In other words, if my top is 94 x 104 I make sure my backing measures 100 x 110.