For some odd reason, I have always been paranoid about this happening to me. So whenever I make binding for a quilt I actually run it along the edge of the quilt with ample fold put on each corner to account for the mitering before I start sewing it on. I have never come up short but I have a ziploc baggie full of "bits 'o binding" ranging from a foot in length to several feet. No worries, I will end up sewing it all together and using it to bind a scrap quilt.