If you have developed the assignment by yourself, the essay exam will be a no-brainer. Just 4 general questions about your assignment: 2 big questions (with a little bit of thought you can guess them) and 2 minor ones (which are random). Try to give as much implementation details (class names, variable names,...) of your assignment as possible to prove you coded the assignment yourself.
No need to be afraid or anxious, it's one of the easiest exams you will get in your life