If you're still at the park, then you might be able to go back to the cast member and let them know and ask for a replacement.
The prize print-out are individually bar coded, so you won't be able to take them back and try again.
If you already left the park, then you will have to try trading people for the gold collection.
Sorry to hear that you didn't get it. I've seen people stand there and go through all the cards front AND back, to make sure it of two things - the card it is supposed to get AND that they can read the code on the back. A few times it was blank or blurred code. So I did the same, I kept a blank one and asked for a replacement, just because I thought it was neat.