fabrics vary in width from about 39" up to 45" for lots of quilting fabrics- it is always a good idea to look at the end of the bolt- it not only tells you how much the fabric costs but also tells you the width, the fiber content, the thread count, and washing instructions-
flannels shrink more than regular cottons because they are a looser weave- it is always a good idea to purchase extra to make up for shrinkage - seems like you could pick up a bit more & piece your backing- flannel really makes wonderful baby quilts.