Hi
I'm pretty sure that the only fix is to put the 64 bit disk in and do it all over.
I don't think there is an upgrade path from 32 to 64 bit in Windows 8.
If you haven't installed a lot of other software it should only take about a half hour to get back to where you are.
Just do a full install so that it wipes the C:\ drive and gives you a clean copy of Windows.
If you have things you don't want to lose and only have one hard drive, you could create a second partition on your drive and move anything you want to keep to that, it will only format the C:\ partition.
But it would be better to have a external hard or second internal drive to back stuff up on.
Mike