I got my code for Flipnote Studio 3D. I entered the code, and then I realized that the code included a Z. I go to check my emails and they didn't send me the code again. Unfortunately the page with my code was closed. The FAQs didn't answer my questions. What a rip-off
I remember that they sent me an email with my Flipnote Studio 3D code, but I didn't receive it for until a day or two after I got the download code. You'll just have to wait for them to send you an email with the code again. If you don't want to wait, you could always make another Club Nintendo account and get another code. It's really easy to make, and you don't have to use your actual email (just create a new email address just for the code). I did that when I was getting a second code for my regular 3DS (my first code was used on my ACNL 3DS XL).
I think you should just wait for the email to be sent, though. In my opinion, Flipnote Studio 3D was really disappointing and useless (at least, useless to me since I can't draw well, let alone animate a flipnote), and this is coming from somebody who used Flipnote Studio on the DSi all the time (though I always used it for Flipnote Hatena). Without Flipnote Hatena, it feels like just another icon on my 3DS, to be honest.
Honestly, Flipnote is one of the worst things Club Nintendo have given away. Considering us Brits don't get it until the new promotional server comes out later on in the year and that's our gift, I will probably just give it away to someone else. Utterly disappointed with the European Club Nintendo anyway. :/