IWill, thank you for the congrats.
As far as dealing with test anxiety, I have a few thoughts.
The more familiar you are with the (agonizing) process of taking the test, the less daunting it will be. I have never been a nervous test taker, but I used to dread Physical Fitness tests in the Army, even though I am a high scorer, because I knew how torn up I would be afterward. Over a period of a year and a half I had to take an abnormally high number of these tests in order to maintain my privilege of designing my own workout regimen, and I just got used to the discomfort afterward. The takeaway: take as many practice GMAT CAT's as you can get your hands on.
If you know yourself and your abilities, that will also reduce your anxiety. I knew my quant would lag behind my verbal, no matter what. I was able to approach the test calmly and actually improve my quant. Also, learn to "talk yourself off the ledge" as it were. Remind yourself that the level of anxiety which you are experiencing is disproportionate to the situation. Be your own coach in that situation; say what would you say to someone else to calm them down.
Lastly, I viewed the GMAT as a set of questions, not a test. The GMAT will not tell you how smart you are or how successful you will be. It will provide you with quantitative feedback based on your answers to 78 questions. View each question as a two-minute exercise. Once a question is answered, you are done with it. It is over- finito. Alright, next question. Remember to focus on one question at a time. Your score is an aggregate of how well you will do on each of those two-minute exercises, but don't focus on the score; focus on the problem that is before you.
I hope this helps. You have shown good perseverance, and I know you can be successful. Good luck!