It sounds like you are doing great, so I'm sure you'll be fine.

I find the opposite technique often works well for me - actually following the "what if I fail?" thoughts and working through the scenario realistically. Fears are often big and scary because we don't really want to think about them, once we shine a light at them they shrink back to something realistic we can actually deal with. So for example if you fail the subject you would need to repeat it, which means it will take a bit longer to finish the course. Which would be a bit annoying, but a long way from the global "I'm not good enough" fears.