I meet a lot of PhD candidates who walk around with a strange indeterminate state attached to their future viva. They think of their viva as pass/fail, not two possible outcomes but a strange quantum state. Until they come out of the other side and know the result, this puts them in a strange too, prone to stress and anxiety.
The outcome of the viva might feel uncertain as it gets closer. You have to have the viva to confirm what your examiners think of your work and of you – but if you’ve got this far, why would the outcome be in doubt? What problems still exist that make the outcome pass/fail? Why do you have doubts?
Explore what’s keeping you in that state. Try to build a good new story for your viva. It’s almost certainly a pass: not because of tradition or statistics or some theory, but because you can’t get this far without doing something good and without being good yourself.
Put pass/fail to one side, and think about what you need to do to change your state.