If it is flat, then no need to block it. If you do have a little ripple after adding the binding, I like to mist the back and pin it square and flat to my spare room carpet ( lay a clean sheet down first) until it dries. Make sure you use rust proof pins and put the pins in the seam line of the binding so no holes shows when it's dry. Don't forget your hanging sleeve or some method of hanging for wall hanging competition.