The Problems
What will they ask?
What will they think?
What will they say?
How long will it take?
What corrections will I get?
What if I freeze?
What if I don’t know?
What if they don’t like it?
You can’t answer any of these questions before the viva. For some of them, there might not be an answer at all as circumstances don’t go that way. You can definitely spend your time thinking, maybe worrying about these problems, trying to anticipate different outcomes. That’s one approach.
Another approach would be to disregard these problems entirely. Instead, spend your time preparing for the viva and reminding yourself how you got this far.