I think it’s you.
Your examiners have your thesis already. It’s possible they have questions about this or that, but if you’ve got to submission and the viva your work must be good enough. Perhaps a detail isn’t quite right, or a paragraph could be made clearer, but you don’t get to submission by accident.
But do you believe that? Where are your doubts when it comes to the viva? What do you need to convince yourself of? How could you do it?
You need to discuss your research with your examiners. You need to explain your thesis and your decisions to them. You might have to defend those decisions in some cases, adding additional support to your arguments and ideas.
But you need to convince yourself: you are the right person for this. You are talented. You are good enough.