I cannot seem to undo the Full-Size View option once I changed it. I was just curious to see what it looked like, but now it cannot be undone.

Its great to see some larger than most images, but torture for images so large it's like viewing it under a microscope.

Where do I go to change this? Or am I going to be forced to make a new account without this option selected?

try clearing your browser's cookies

Lol, one of the first things I did.

I've emptied my cache and browser history, used my VPN in case it was a IP signature issue, tried incognito, and even logged in with a different browser.

After trying all the most obvious routes I figured there was something more I'm missing.

are you sure you cleared your cookies?
as far as i can tell this is an entirely cookie-based feature, so double-check that

you can also try running the following code in the web console of any rule34.xxx page:

document.cookie = "resize-original=0";
document.cookie = "resize-notification=0";

Get cc cleaner and clean out your browser cache also.