the thing about unsewing is that the fabric gets skewed out of shape. so even though it looks the nicest, is it really the best idea to take so many pieces apart? this is more than one or two pieces here. one solution may be to find another totally different fabric that coordinates and add the extra length top and bottom before adding borders. another might be to use the same solid colors in a different but coordinating pattern, like three rails across then three rails up and down, in two strips, top and bottom, before adding borders.
what is the width of the quilt as it stands now and what do you shoot for?