If you don't have a previous save that you can go back to.
C:\Users\<Username>\Documents\Electronic Arts\The Sims 3\Saves
NameofSave.sims3
NameofSave.sims3.backup
If for some reason you do find a NameofSave.sims3.backup. Make a copy of the file, and then rename the copy. NameofSave2 and try to load it.
You may try looking in the Household bin, or Sim bin to see if they've been save in one of those places?
The Household bin is the "white house" in the user interface - like in the photo below:
Household Bin
The fastest way to find the Premade Sims saved in the Sim bin, go into CAS and click the 6 Sim button (photo below) and then click the asterisk (*) up in the right hand corner of the menu. 2nd photo below.
Premade Sims
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