Your situation is almost the exact same as mine!
I too, did reasonably well IN school.
I can tell from your writing style and proper grammar
that you ARE intelligent -- as am I.
I also failed at 75 questions and had NO IDEA I had performed so poorly.
Your KAPLAN scores are also similar to mine.
So understand when I tell you, "YOU ARE NOT ALONE".
I have the same overbearing feeling of doom when I think about my failure. Obviously, I was too confident!
I keep wondering to myself, "How can I fix whatever is wrong with me?!"
It literally keeps me up at night!
My advice (and what I am currently doing) is to forget you ever took it and failed. Pretend it was a practice exam and just learn from it. Do at least 50 questions everyday from now on.
Do not doubt yourself! You are intelligent! You did learn during class and clinical!
And just kick-ass the next time around.