If you are worried that you might finish on the position of 2nd,3rd or 4th place, and the opponent cars might catch up to you, hit the R button to use the Nitrous Oxide which boosts the speed of the car!
Hope I Helped!!
Here are a few tips:
1) Almost every level has a shortcut, but if the difficulty is on hard, the computer cars will use the shortcuts.
2)You get the Aston Martin FREE if you beat the game.
3) To accelerate much faster, hit the gas just as the one fades away at the cowntdown.