The racing world is where the toughest guys all participate. They need to be tough as the road is as tough as can be. If you are not up to it then this might be the last road that you might see. Aside from being careful, you also need to have the strength and endurance to keep up with the racing course.
Drive as fast as you can till you reach the finish line. Grab those time on the road as that will extend your time. The booster slowly refills, so there is no need to hold out on using them. Just use it whenever it is available as you need to outrun all the other cars in this race.