If you figured out how to get to submission then you can figure out how to succeed in the viva.
If you did all the work and wrote it up in your thesis then you can discuss it with your examiners for a few hours.
If you spent three (or more) years doing the research then you can talk for three hours (or less) about what it all means and how you did it.
Beyond nerves, beyond expectations, beyond the details of your research and your story, this is what it all comes down to. We can find lots of ways to look at the situation but it’s quite simple.
If you did the work, then you’re good. If you’re good then you can pass the viva.