I really really wish we would get another empty world.

@ EdithV ""Can it delete your other worlds? Also can you use an old save or do you have to start a new one ?""

Nope, it wont touch the original Maxis worlds at all.
But, if the instructions are not followed, it can duplicate the world completely rather than simply make an empty copy.
Fix is simple, shut down the game and restart.

And Yes, I would suggest using a new game rather than adding to an existing game for a first try.

That said, I now have every ingame world copied and renamed, still no idea why. But, it works.