"Prove up"? Is this a Prince Hall term? Or a regional Washington one? I'm just curious.
What I was told, and what I in turn tell candidates is, in no uncertain terms, everyone here wants you to succeed. Because everyone there (and here) does.
I'm not sure if in your jurisdiction if you are permitted to use a book or some other printed word as a learning aide. If you are, and if you are using it, then set it aside and focus on working in front of another person, with other people, at all times.
Your instructor should know when you are ready to go. You do have one assigned to you, yes?
The bottom line is that by the time you are examined, you should have many hours of real world practice in front of other people. Repetition, in simulated circumstances of your examination - thats how you overcome nerves.
Public speaking is the #1 fear in the United States, above heights and so forth - for good reason. Repetition is the key - it makes it routine, and routine things you can manage the nerves for a lot better.
Also, consider learning the work to a higher level than you need to know it. For example, if your lodge does not require you to learn the questions - do it anyway. Don't deliver it that way in the examination, but know, in your bones, that you could. That knowing you know the work cold, 110%, removes doubt.
Ask yourself, could you teach the work to another person? Without the help of a book or something? If the answer is no, then get to the point you could. That extra confidence will silence the mind when you hit a snag and allow habit to work.
All the way around making that the goal, to get to the point where you could teach someone else is a great goal. Some of the best teachers in every field have struggled the most. Because they have had a setback, they can relate to their pupils, and understand their fears and challenges better than anyone.
It might be helpful to you to decide to be one of those type of people.
Good luck, Brother.