You're fine, OP. I did the same thing about a month ago. Email support and they'll ask for a photo of the front and back of the card and your account info, they will most likely credit your account with the money if everything looks legit.
Same thing just happened to me. Why the fuck do these fucking idiots design the cards so that the code is so easily damaged? And Nintendo's support is closed so I have to wait until tomorrow. Le sigh.....