The Sims 4 – Transferring Sims from the Demo to the Base Game!

Any Sims that you uploaded to the Gallery in the Create A Sim (CAS) demo must be downloaded from the Gallery in the full game. Households that are just saved to your Library will not be available in the full game until they are downloaded from the Gallery.
 
If you are not finding your Sims, it could be due to one of the following issues:

The CAS demo and The Sims 4 are on separate Origin accounts.

• If your demo and base game are tied to different Origin accounts, then your Sims from the demo will not populate into your base game Gallery.
• The easiest way to get your Sims is to upload them to the Gallery from the CAS demo. Then you can search for the proper Origin ID in Gallery and  download them in The Sims 4 on your other Origin account and download your Sims from the Gallery.*

 
The CAS demo and The Sims 4 are on the same Origin account, but the Sims were never uploaded to the Gallery.

• If the demo and base game are tied to the same Origin account, it’s likely that your Sims were not uploaded to the Gallery. Sims that are saved only to your Library in the demo will not display in the full game.

• The easiest way to get your Sims into the full game is to just upload them to the Gallery from the demo and then download them into the full game.* Otherwise, you can copy the files fromDocumentsElectronic ArtsThe Sims 4 Create A Sim DemoTray to DocumentsElectronic ArtsThe Sims 4Tray in order to “move” your Sims from the demo to the full game.

Via EA Help