Autosave intentionally does not leave a backup, because it already sequentially rotates autosaves. Making a BACKUP of a BACKUP save would be RETARDED.
So there IS a backup, if that option hasn't been set to only one autosave. As I understand it, autosave keeps two saves, by default, and alternates between then.
OP: So, then, try the second save, not the most recent one. If you've disabled the option, or told it not to keep a second save, then I'm afraid you can't recover your game.