It will run backups as scheduled if you are running it as a service. You do not want to open the Duplicati icon on your desktop. The only reason that seemed to be necessary in your case is because only that user instance was configured.
Since it was just a test backup you can probably skip a lot of my steps. Stop Duplicati (the user instance one) and delete the /home/user/.config/Duplicati folder.
Then access the service UI by going to http://localhost:8200 and configure a new backup job. Whenever you want to view Duplicati UI just go to that URL - don’t use the icon.
Let me know if you have any other questions!