I did some calculations and the original with 40 strips comes out about 50" x 64"
This is using 40 strips at 40" long.
I tried other combinations by reducing the number of strips and they all come out much longer than you want
the closest was 31"x62" if you reduce the number of strips to 25. Seems the math and length works against precise sizes that is unless you want to do one the closest size you want and then trim some off the bottom.
This might not be a bad idea as you could use the strip to add to the backing fabric for a creative touch.
Smeone may have a better way to calculate but my grade school math just doesn't make it work. I might tend to just sew the long strip together and rather than double back for the next strip to cut it off at the size you want and add the other trips.