First of, if you somehow don't have a backup of any of the files, it is hard to imagine you can get a your "deleted main back".
Next:
(a) how are you playing the game. Emulator, retail device?
(b) how are you getting the save. Homebrew, accessing the emulator's save folder etc.
(b part 1) if on retail device, and extracted the save using homebrew, how are you transferring the save to your computer?
(c) how are you saving the game. Are you using the in-game save feature to save the game. (Open the menu in the game -> hit Save)
Make sure you answer all parts above.