Try not to panic, first off. I know something you'll get marked down hugely for, as it can impair your communication, (which was 30/60 marks for my exam board) is rushed speech or panicking and saying 'wait' or 'what' in English. I was so nervous for mine, but managed to get 60/60 (somehow???) so I really hope this can help.
So long as you've written it well enough (idioms, a range of tenses and vocab etc.) all you have to worry about is memorising it and reciting it at a steady pace. Literally all I did was read mine over and over, speak it to myself, then read it over again. Make sure your pronunciation is correct (Google translate audio can help with that) and you're not making silly errors with grammar - your teacher should've checked that over for you. I would just sit for an hour and get a few questions out the way every day.
Once you've memorised it, it's simply the recital. So long as you're calm and collected, it should be difficult to drop marks for communication. If you make a mistake though don't panic, as you can still get a great grade.
As for the unprepared questions, think logically about what they could be, and prepare yourself with some simple vocab on your topic. Mine was on holidays, and one of the unprepared questions was 'what did you eat for breakfast', after she asked about my first day on holiday. My answer was something simple like 'we ate bread and cheese - it was delicious'. That's all that was required, so don't panic about those questions. What's far more important is the learning of your actual assessment.
Good luck!
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