Overcoming Self Doubt

I'm not a person that usually doubts myself. I'm very opinionated and sure of my beliefs. But for the last few days I'm having a crisis of faith.
I'm convinced I'm going to fail my VTNE exam.

I've been studying and reading and thinking about stuff at work for months. I've gone into Defcon 5 mode now, since the test is less than 14 days away. I've even started to review the math questions that I forgot how to do, and feel a lot more confident in my calculating ability.
Yesterday I took a practice test, straight from the Technician Review book that is one of the texts I'm studying. As I answered the questions I felt confident. I felt that things were finally coming together. I could even do the math.
My grade was 70%. When I first started taking the practice exams my grades were in the 60's. How can I feel so confident and yet not get more than 70% correct?
So last night I gave up. I went to my bookshelf and grabbed a fiction hardcover that has been waiting for me to read it, and I immersed myself in it. I sulked and posted a pity status update on FaceBook. I told myself it didn't matter if I passed.
What is wrong with me?
I woke up today with the attitude that I only have a few days left, maybe I should just go ahead and keep reading/studying. Who knows what the test will be like? I have to make the best of things, since I devoted so much of my time and energy to it. I know it's not the end of the world if I don't pass, and my friends keep telling me I can take it over (but I'm not sure if I can, due to new regulations) , but I know in my heart I have to give it my best shot.
I will read over the chapters on diagnostic imaging tonight, and do math problems every day until Dec 8th.
I may or may not take another practice exam. I WILL try to put all negative thoughts out of my head and rely upon my intelligence and natural self confidence.

I just wish it were all over already.