Why do I feel like I will fail, if I don't know what is going to happen?

People sometimes feel overwhelm by things. They tend to overthink even if it is not yet happening. Try to be calm and focus, do all the preparations you needed before doing something. As long as you know, you give your 100% best of your best and you are well preapared there is no such thing to be worried of. I guess, its normal for people to worry for the results of something butn like I said. Make sure to prepare, do all things that you can do to study and plan what you are going to do, be patient, be consistent. And if you think you are ready and well prepared it is time for you to do what tou have to do. What matters the most is the preaparations you did before it. Everything will be fine.