The purpose of the exam is to assess your knowledge and verify understanding of the training course. However, the purpose of the training course is for your educational benefit. Therefore, you are allowed to take the exam twice, if needed.
If after taking the exam the first time and you are not satisfied with your score, go back and focus on those areas in the module where you missed questions and then review the information. Then, you are free to take the exam a second time. If you choose to take the exam a second time, your score for the first attempt will be wiped out and your final score will be the score of the second exam.