Hi!
Stress and anxiety - seems to be a very common theme, at least among myself and all of the GMAT-taking friends. I'm going to be honest with you - it's difficult not to get stressed out before important tests. However, I can tell you that all of the following helped me keep my mind where it was supposed to be in the run-up to the exam:
- Don't interrupt your normal schedule. You've said that you haven't been skipping workouts, which is very good. I would encourage you to surround yourself with small, interesting projects at work, and try to feed off of the satisfaction of completing tasks quickly.
- Instead of focusing on counting down the days, do as many problems as you can get your hands on. Personally, I would do 3-4 hours a day each day after work. By the time I was done, I would be exhausted and ready to go to bed. This stopped me creating the old self-fulfilling prophecy where you start to doubt your own ability.
- On test day, I ran small errands: going to the store to buy energy bars and a big bottle of gatorade, cooking some fish to eat, and filling up my car with gasoline ALL helped take my mind away from the GMAT.
The most important thing is this: you must possess no doubt at all about your ability to answer questions correctly on a consistent basis. If you have even the smallest amount, run it out of your head by doing as many practice questions as you can get your hands on (preferably from official sources, although I find that a lot of stuff floating around this forum is very useful, too). All disastrous experiences come into being from something that is very tiny to begin with, but is not taken care of. If you're scoring 680 in your
MGMAT and Kaplans, then you have no business scoring 540. It's an anomaly, and you have to continue telling yourself that. You should go in knowing that you will get questions wrong - but you need to have every confidence that this is not the norm, but the exception!
As for the beta-blockers - I know for a fact that you don't need them, because you're confident when you take the test at home. If you were a sobbing wreck upon seeing the words GMAT on paper, maybe that would be a different story. Right now, you have to spend less time dreading the test center, and more time drilling all of that knowledge into your (already reasonably full) head.
Think of how professional boxers do it - they're all terrified of having to fight, but they chase it out of themselves through ultra-rigorous training that leaves them craving the adrenaline that the fight will bring! If you can get into the same mindset, you'll be scoring 700+.
All you gotta do is believe in yourself!
Oh - and one more thing. Spend a bit of time practicing for the AWA and IR sections. Writing a good essay and doing some compound problems can drain the fear out of you much faster than only spending 15 minutes on each. Trust me.