You mean that you copied the 3-section code onto the Storm 3 website, and you didn't write down the code to use for Marketplace/PSN?
There's an option where you can get an email sent to you with the code, just incase you forget it. It sucks that they don't do that automatically, tbh.
If you have already redeemed the code on the Storm 3 website, I don't think there's anyway to redeem it again. You can try contacting Namco-Bandai customer support and provide them with the code you used. Then, they should hopefully send you the code to use for downloading your costumes.