I don't want to give spoilers, and I do believe there's no way to go back and get the code again, unfortunately. That's a really unfortunate situation and something I'll have to account for in future games. Sometimes people have to step away from games and didn't have the foresight or even the spare seventy-one or seventy-five seconds it takes to write down a four -digit numerical code.
Sorry if that sounds snarky. I sincerely don't mean it that way. It's meant to be helpful. ;)