Consider reading a book called "The Now Habit". The author discusses fear of success/failure and the inability to finish projects, and deems that these fears are what cause us to procrastinate. Then he provides a plan/approach/framework to overcome these fears.
Thanks for the book recommendation. Ordered this on Amazon.
This was my problem all growing up. I did well on the first exam, then fizzled out every exam after. I wouldn't study out of fear that I wouldn't do as well again.
I'd recommend Mindset by Carol Dweck. It discusses growth mindset vs. fixed mindset. It sounds quite pertinent for your fear of not doing as well again.
I second this book recommendation. I read it a few years ago and find myself referring back to it quite often for inspiration when I'm feeling unproductive and very procrastnaty.