Being prepared by practicing on simulated situations with challenging lighting conditions will infuse you with confidence. Do a series of test runs of every type of photography job that you dream of doing but fail to pursue.
Take a deep breath and believe this in every molecule of your body. Everybody fails at some point in their lifetime – absolutely everyone.
No one is perfect. No one makes the optimum decision every single time. And most of the time, falling flat on your face and failing teaches you some valuable lessons that you needed to learn.