If you did your best to write a complete, clear, and insightful essay within the time allotted, you should have nothing to worry about.
Unless if you finished way ahead of schedule, don`t worry about major revisions like reorganizing the structure of the essay–it`s better to hand in an essay with an imperfect structure than a paper that`s impossible to follow because you had to stop halfway through the revision process.
Therefore, if you take the time to review your notes and ensure you understand everything that was discussed, it should be difficult for the essay question to catch you off guard. As soon as you read the question, relevant course concepts will start popping into your head, and you`ll just have to organize them into a coherent essay.
When composing essays, many students stop and read over each paragraph once they finish it, making sure that it`s well-written and free of errors before advancing to the next one. This approach is entirely logical when there`s no time pressure involved, but it can actually work against you during an exam.
For this reason, it can be helpful to simulate the conditions of a timed exam before the actual day: pick a practice question, find some lined paper, set a stopwatch, and see how you do!
Decide on your thesis, the topic of each paragraph, and the arguments which you intend to cover, then jot down some quick point-form notes. This process won`t take long, and, once you complete it, all that`s left will be to expand those notes into a well-organized essay.