Need help restoring version of a doom level

[A Dense Goblin]

Hi. I'm making a doom level and while working on it I decided to try and add some custom music. The music worked . When I was doing this, I had Slade and GZDoomBuilder open, but then I took a break. Later, when I got back on, I decided to change the MIDI, but in a stupid lapse of judgement, I had closed GZDoomBuilder but not slade, and I saved the version of the level that was on Slade, thus kind of undoing a lot of progress in the level's geometry. I don't want to spend 2 hours redoing it so is there some sort of recovery feature?

[Marcaek]

I don't remember if I had to enable it manually or not, but check the folder you saved the map to for a numbered "backup#" file: there should be up to three with your map's filename. Rename it to a new .wad file and open.

[Gradius]

Look for .bak files in the directory you saved to. Rename them something different and end them in .wad.

[VGA]

To avoid this in the future I think you open the wad in SLADE, right click the map and use the "Open in Doom Builder" option. Personally, I keep the resources in a wad and the map(s) in another wad. If you plan to release the thing then you combine them.