When applying your borders be sure to follow these steps:
■measure the width in three areas, average the width (41″, 40″, 42″=41″ for each border)
■cut two pieces at 41″
■pin and carefully sew, press
■next measure the length, following the same instructions above
This will ensure a square quilt. After the borders are applied and pressed, take these measurements and add 8″ to the width and 8″ to the length for your backing size. So a 70″ X 70″ quilt will need at least a 78″ X 78″ backing. The reason for this is I pin the quilt backing to leaders adding the batting and next the quilt top. Remove any selvages from your backing.
This is what I suggest to my customers... Take the time to do this and you will be a happy camper.