I did the Prairie Star a couple of years ago ... my first, and so far only, JM pattern. I tried to follow the directions as much as possible, since it was my first one. Even including all the plastic bags! Seemed like there was quite a bit of overage -- like sometimes you cut a WOF strip and only use half of it. So I'm guessing you'll be fine if you have the yardage that the pattern lists.
Good luck!