PamNewman, that information won't be available to us until the very end.
However, the quilt is 86" square. So, if you guess the last borders are maybe 5" wide each (they may be more or less than that, I don't know) that would make the final red floater about 76". If you buy 2.5 yards, you'll have 90" which would be plenty. You would not have to piece the floaters and can use the extra fabric for the binding.
Just a thought...