Yes, you can cancel it and be issued a new one.
My blank money order was stolen. Can I cancel it and be issued a new one?
Yes, you should be able to. As long as you kept the reciept. If the money order has been cashed, it may take some time to get a refund.
I really don't know, I would think that you could, but this is something you need to discuss with the company that the money order was placed with.