Studying can be a situation that triggers thoughts that trigger performance anxiety. Performance anxiety is very common and easily treatable. One of the things that is at the core of performance anxiety is that "I must be perfect all the time" this thoughts adds lot of anxiety. This anxiety contributes to your mistakes and you negative belief gets strengthens.
Next Steps
See a psychologist. Focus on the process and not on the end goal.
Health Tips
Avoid thinking about being perfect. Perfection is a myth being appropriate is the reality.