I've heard repeatedly on this forum and others that someone should expect to drop 3 or 4 points from their Testing average on the actual test day (because of nerves, new environment, etc).
I just want to suggest that this is a really self-defeating thought to have in your mind. I'm not saying don't be prepared to potentially do worse, but also don't go in assuming a 3 to 4 point drop in score. I've met at least 5 people that have told me they PEAKED on test day. That is, they scored their highest on test day, sometimes 2 or 3 points over their normal prep test score.
I'm not saying you should go in assuming you will score 2-3 points higher on test day, but I would suggest orienting oneself around a goal of peak performance instead of an assumption of dropping points.
The mind is a powerful thing.
Consider an Olympic athlete. Many athletes have "Peak" performance on the actual day of the Olympics, getting better and faster times than they ever did in practice. Some get nervous and do worse. Point is, it can go either way. I'd aim for thinking about Test Day as your peak day.
Of course work hard and get the best average score you can before test day, and be prepared for anything, but go into the test aiming to peak.
Just my 2 cents.