Your top is 1/4" larger than what you wanted? Are you using two solid color borders....red, then white?
Have you measured the quilt in three places...top, bottom and middle? Is the difference the same on all three measurements? If not average it out...then I would sew both borders together to that measurement, then add to top, making sure to center and pin down, mitering the corners...less change of getting waves between 1 st and 2 nd border...just my thoughts on subject