Hi from Alabama! You will enjoy the friendly atmosphere here....and we will help you all we can, if we know the answer. About prewashing fabric, like NJ Quilter, I only prewash the darker fabrics, like red, black, and dark blue, and I have washed some teals before using, and I was glad I did. It bled into the water pretty bad.
Also like NJ Quilter said, the easiest way to make your quilt larger is to just make more blocks until you get your quilt the size you want it.