Can’t redeem giftcard

I have a gift card from a while ago and just peeled off the silver rectangle on the back. I went to iTunes> redeem> and used the camera to scan It but I clicked the “back” arrow in the upper left corner instead of “redeem” in the upper right corner and it took me back to the redeem screen And the $ has not been applied. So I did it again and now it’s telling me that the gift card has already been redeemed.

Please advise.