Some of the last test items may have been easy to answer, but you never saw them, because you got hung up on an early test item. This is also good advise for essay questions. Answer the easy ones first, then return to the hard ones. If you should have time, scan over the exam a third time to be sure that you attempted every test item unless you are penalized for guesses. A word about the time for an exam.
Most exams have a time limit.
That can be good provided the time is sufficient for the given length of the exam. It will provide a tolerable stress level which should stimulate your mental processes. Worry will only raise your stress level and take your mind off the next class. You can't change the result of your exam by worry, but you can adversely affect your performance in your next class. Take a positive attitude before and after the exam.