When you complete a distance, you only get a reward for the distance, not for the place in the leaderboard.
The distance reward is shown at the top center of the race window. But you will receive the reward from the box in the ranking only after the end of the competition. The reward will correspond to the place where you will be at the end of the competition.
If you have not received a reward after the end of the contest, check your inbox in the game.
If there is no reward in the inbox, please contact support service.