As a LA'er point of view, I would take them off and do the measuring and resew them. It makes it very hard to do quilts that have boarders that are wavy, and it will be out of square for sure. You might have to trim alot of the boarder after the quilting to get it square therefore they will not be the same width on all sides. I have never gotten wavy boarders when I measure in the center and then carefully pin at each end and middle then pin very closely inbetween those points. When we get a quilt in thats like that we always attach a sheet of instructions on how to properly do boarders for the customer to use later !!! Sometimes there have been some that are so bad that tucks have been done to ease in the boarder.....Its worth the time to re-do them and get used to doing them properly in the future you will be happier with the final product....