Peachey is right, get a good sleep, relax. At most, watch a movie in English.
Examiners like candidates who speak naturally, and smile sometimes. They do not like robots. It's ok to make mistakes - and it's great if you know you've made a mistake and smile, and say, "Oh dear, I think I got that wrong, let me try again," because examiners love that natural use of English. It's what any of us would do if we made a mistake, or didn't understand the question, or forgot it halfway through the answer! "Oooops! What was the question?"
So be YOU, speak clearly, and be as natural and relaxed as you can be, under the circumstances!