If you really want to use a particular fabric but don't have quite enough to cut in half then stitch back together to make a wide back, there is a way you can cut the fabric on the diagonal to make it work. It's difficult to explain in this short space, but you can check out John Flynns web page where he explains it and provides instructions that you can print out. It might help you out sometime. The link here is to the home page. For the information on the diagonal cut technique, go to "John's workshop" then to "free lessons" and scroll down till you find it. You might also get a kick out of how he used a weedeater to make a rag-edge quilt.
http://flynnquilt.danemcoweb.com/