Help me

If you can read this, help me. I was trying to put The data for the last hard mode level into the first boss level, and I screwed up. the level doesnt work, and I can’t complete it, and now marathon mode (which I beat) is now locked. I tried to get the code for the first boss level back (I put the data on a notepad) and I took it off the notepad and put the data back. when I went back into the game, the level hadn’t changed. Can you please comment telling me how I Get the code back?