The races may seem a little difficult to start with but as your progress in challenges you will earn speed bonus's so you may want to leave the races until you have made some progress within the story challenges. Once you're more comfortable with the controls you will feel more confident with the races.
While racing pull back on the to speed up and the to slow down. Avoid as many jumps as possible. By the time you have played through each race a few times you should be able to beat the pros without any issues.