Accept the fact that after exam time, things are out of your control. You did the best that you could on the exam, and no amount of worry or stress is going to change the end results now.
Avoid going over the test questions and answers in depth until after you get your exam back. Doing so now causes more stress and makes you second-guess yourself.
Find out when you can expect to get your exam results back. Write the date on your calendar. On the day before the results are coming back, make a note on your calendar that you can worry. Give yourself permission to feel the stress for 24 hours before getting the results back so that you feel free to set aside the worry for now.
Choose a healthy release for the adrenaline. When you are studying for an exam your body prepares for fight or flight the same way that it does if you are facing a physical battle. When you take the exam, your body goes into fight mode, but you do not get the chance to physically release the adrenaline. Post-exam, go for a walk, a run or work out at the gym to release the adrenalin and calm your nerves.
Distract yourself doing other things until your calendar tells you it is now time to worry. Worry for one day waiting for the results of the exam. While you are worrying, think about what options are open to you if the results are not as good as you hoped. Make a plan for dealing with bad result in case they occur.