Instead of wondering if your thesis is good, first ask yourself what you look for in a good thesis. What do people generally want?
Instead of worrying about what questions your examiners might ask, start by thinking about what questions would be in your mind when you first pick up a thesis. How would you start to unpick a large book of new research?
Instead of hoping you’ll be ready for your viva, ask what you would need to feel ready. What would you need to have or be to feel confident on viva day?
Whenever you encounter a doubt, flip it around. What can you do about it? Got an idea? Go do it.