I always do a colorfast test and find I rarely need to prewash--take a piece of white paper and rub any suspect fabrics very hard--if there's any color on the paper--wash, otherwise you're safe (although I use a color catcher anytime I wash a quilt no matter how often it's been washed). BTW--this color fast test was shared by a LQS owner. since I don't prewash, I save my starching for when I know I'm going to be cutting lots of bias edges. The sizing in the unwashed fabric gives it enough "stiffness".
I agree with PaperPrincess that cotton sateen seems to have more stretch in it--so if yours is that way, a wash and dry ahead of time may shrink it so it's not so stretchy--not a game changer,but do be aware. Can't wait to see!