I redeemed a gift cart onto an account that I forgot the security questions of.

Have you tried getting the questions reset on that account by following the instructions on the HT5312 page that you posted from ? i.e. if you have a rescue email address on your account then steps 1 to 5 half-way down that page should give you a reset link.

If you don't have a rescue email address then you will need to contact Support in your country to get the questions reset : http://support.apple.com/kb/HT5699

When they've been reset (and if you don't already have a rescue email address) you can then use the steps half-way down the HT5312 page that you posted from to add a rescue email address for potential future use.

If you want to move the card to a different account then you will need to try contacting iTunes Support and see if they can move it for you :http://www.apple.com/support/itunes/contact/

With security questions they need to confirm your id and that it's your account, which is more easily done by phone - you can try contacting them via this form, but they are likely to reply (and it might take 24 to 48 hours before they reply) asking you to contact them via the link/number on that HT5699 page : https://ssl.apple.com/emea/support/itunes/contact.html