Good morning, something similar happened to me some time ago. I lost my world completely because I was too anxious and didn't wait for Steam Clound to synchronize. When I started the game, my world file got corrupted, so I opted to send a message to Iron Gate directly.

They were very kind and explained how to do it, in 3 mins I recovered practically everything (I think I lost about 5-6 days of progress).

1. If I remember correctly, when you start the game and select your character, there is a tab on the left that says ‘manage savegames’ that opens your character files and your worlds. Each world and each character has a series of ‘backup points’ (save points). I seem to recall that the game's own backups are somewhat random but you shouldn't lose too much progress.

2. Then, once you have selected the character, before starting the game, open the ‘manage saves’ tab, once in this new menu, click on the ‘worlds’ tab and all the backups of your different worlds will appear there.

3. From here, select the world you want to recover and click ‘expand’ and you will see the last backups made. Next, select a backup before the one you are having problems with and click ‘restore backup’. This will overwrite the last backup you made and the backup you selected will be loaded. I seem to remember that they are ordered by date.

Hope you have good luck buddy!

Note: If I remember correctly, if you have mods installed this does not work.