Need for Speed Carbon Problems?

I've pretty much beaten the whole game, except the last two races against Darius. The city circuit race took me about 10 tries and then the Canyon Duel was practically impossible. I kept falling off walls. I've probably tried about 98 times. The car I use is a Plymouth Hemi Cuda. The accel is maxed and handling is only half full. The top speed is 172mph. I've been able to am about 105g on the first run but Darius' score is better or I fall off those darn orange walls before the run is over. Can someone plz tell me what I'm doing wrong