Go back to the Options screen by press Left, X. Now set Difficulty to Professional and Trophy Presenter to "Rider's Choice". Return once again to the Main Screen and press Up, Left, Down, Right, Up, Left, Down, Right.
If you did everything right you'll hear "Ka-ching!" and gain access to all the tracks!
Alternatively, go to the first ramp (not the broken highway) and gain as much speed as possible. Once you're on the ramp, pull off on the side with the black line. This takes practice, but if you get it right you'll sail over the bouys and can drive around outside.