Don’t be. After years of research and months of writing, it could be hard for you to see someone else’s point of view.
But it’s easy to imagine your examiners will see things differently to you. Maybe they have a relevant question you’ve not considered. Maybe they don’t quite get what you mean. Maybe a section of your thesis that is perfectly clear to you is only clear because of everything else you know.
Get other perspectives before the viva. You don’t have to change your perspective on your work, but it is really useful to consider others. Get feedback from your supervisor to see if there are other approaches or considerations you’ve discarded. Get questions from friends to help explore around your topic. Write summaries of your work to draw out ideas and make your thoughts concrete.
Don’t expect your examiners to know more than you, but don’t expect that you know every possible question or idea either.