The book says about prewashing,
There is no need to prewash the fabric. This removes the sizing and can distort the fabric. You can begin cutting into your fabric as soon as you get home!"
Further she states about the fabric,
Do not buy fabric from more than one bolt. Sometimes you find the perfect fabric, but there is only a yard or two on the bolt, so you go to the internet or to another store to buy more of the same fabric. This will not work. There is no guarantee that the colors or print of the pattern are exactly the same from bolt to bolt.
M