Stressing out about something as important as the bar exam is perfectly natural, but why do you feel the need to talk yourself down? You've obviously worked very hard to make it this far, let alone the fact that someone with a disability has to work that much harder to keep up, and you've proven yourself more capable/hard-working than 99.99% of humanity already.
While I can't speak from first-hand experience about your situation per law school, I don't think you should let perfectionism sabotage you. If you pass the bar, you pass, even if you don't "make history" and be one of those A's, pulling off even a C is still a pass, and you can move on with the next stage of your career. If you don't pass, then take a moment to compose yourself, go back to preparing, and sit for the next exam. Obviously don't take my advice as encouragement to slack off or anything, but I seriously think you will do better on it if you celebrate your accomplishments and not worry about the possibility of failure.
Just keep remembering that stress originates from within YOU, not the environment. That fear of your brain "crapping out on you" is your nervous system being kicked into high alert. You have enough self-discipline to make it through prep education, university, and law school, you've proven that already; you certainly have the discipline to reign in the stress and achieve your potential.
Just some encouragement, good luck on your bar!
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Viva la raza, Death to America, Allahu Akbar and all that
Your Aspie score: 92 out of 200
Your NT score: 107 out of 200
You seem to have both Aspie and neurotypical traits
Diagnosed AS, OCD, ADHD