If you have spent your time procrastinating then start now. It's okay, you kept thinking that you will do it later since you had time. Start with the an interesting topic to gain momentum. Now, write down the list of topics you would be able to grasp that are useful for the exam. Do active practice, write them on whiteboard (if you have one) or a simple paper and read out loud. Do not keep score too high. Increase goal with preparation.