You have earned a gold medal in the final scenario in Champions Mode.
The last scenario will only be unlocked after you progress through all of the first 6 challenges.
To get a gold medal on any challenge you will need to complete it on Hard difficulty. You can have as many driver assist as you fell like, but I recommend getting Pit Assist and Braking Assist off. Try getting your fuel mix to Rich as quick as possible to get the edge as you will not be able to change set-ups or do much change on the car.
It may take you a couple of tries until you are familiar with the circuits and overtaking positions.