Take it back. I used to think once it was cut you were dead in the water but not true, Joanns is pretty good about taking fabric returns. I stood in line behind a gal who was returning fabric because she had asked for 3 yds. and the gal cut 2-1/2! And, of course, the receipt showed 3. I've found you really have to watch the gals cutting at Joanns and if you think they are screwing up, make them do it again right there.
I didn't question several cuts until I hit the cash register and the poor guy cashiering had to go back to the cutting table to resolve the problem - the cutter had made mistakes on every piece of fabric but fortunately, for me, I was clearing bolts. What she couldn't get right was the yardage she had measured!