What's you IGN? Hmm, maybe I miss yours.

Neway,
Found this while doing the power parking challenge. Every time sure got 100%, coz the ramp stop you from going further. As long you didn't hit the parked car, you'll getting 100% over and over.

Well, some how-to from me.
To do the double barrel rolls, hold the left or right key (depend on which way you rolls) while you're rolling in the air, since the game will auto-correct your car after 1st barrel roll. Pressing the arrow key will force the car to rolls again.
To do power parking, find any empty space between parked cars, and do e-brake. Make you car as parallel as possible. It'll be quiet easy once you get hold of it.

To do flat spin, hit e-brake the moment before you jump off. You car should be spinning mid-air.
To drift, well, hit brake while cornering.

So I hope we can do the challenges properly next time once everyone knew this.

Anything that I miss?

Thanks for the guide. Yesterday was wondering how to power park. I thought need to go into a parking lot and park.
We need more challenges next time. It is fun!