Screenshots are from a Model S, but it should be similar on the Model 3:
Select "Autopilot" from the settings menu:
View attachment 463110
Activate "Mit Autopilot navigieren (Beta)"
View attachment 463111
Select "MIT AUTOPILOT NAVIGIEREN" ANPASSEN
& select the options
View attachment 463112
When activating a destination in the Navigation you should get the NOA option
View attachment 463114
But prior to NOA, "Lenkassistent (Beta) must be activated
Then you should get 2 blue lines when Autopilot is activated.
View attachment 463118
or 1 center blue line when NOA is activated (only when driving on Highway)
View attachment 463115