Careful measuring is a key component of making a square or rectangular quilt really square or rectangular. Never measure for borders on the edge of the quilt. Measure in more than one place. I actually like to measure at the previous seam line because it is stable at that point. Then I cut and fit (pin) the border in place by finding the center and quarter points of the quilt and the border and pin in place before sewing. Make sure that the parallel sides are alike or the quilt will hang crooked. On most machines the bottom layer will pull through the feed dogs at a slightly different amount than the top layer-giving a larger perimeter. This small, but significant, increase will be magnified if there are several borders. Another tip for keeping this increasing lower layer creep is to use a walking foot to sew the borders onto the quilt-it allows the fabric pieces to feed evenly through the machine.