For future reference when making a string quilt like this, consider using the 'self-sashed' method of putting a 2inch strip of the same fabric down each center of fabric diagonally. When you put the blocks together that diagonal fabric creates an on-point 'sashing'.
I do it all the time and I use the cheap muslin or ugly fabric wrong-side up as my foundation.
here is a photo, hope the link works
http://thumb5.webshots.net/t/72/172/...5gEHgwx_th.jpg
warm quilt hugs, sue in CA