Walmart is usually pretty good about returing stuff. Especially if you have your receipt.
I've returned fabric there before because it didn't match what I needed it fot when I got home, so they should for sure do it with something like that!
They will take it back to the fabric Dept. and measure it to make sure its still the same size you paid for. If its not, then they will only refund how much you have with you. For example, if you paid for 3 yards but only returned 2 you will only get the money back for 2.
I've sent you a pm, also.
Good luck!