Is passing your viva guaranteed?
No, but let’s say that it is the most likely outcome. Statistics, stories and the structure of the PhD journey say it clearly: how else could a candidate get to submission if they and the work weren’t good and ready?
Passing is the most likely outcome – many, many times more likely than failing. You should not expect to fail. If you feel really worried, dig into that. Why do you feel that way? What’s the problem? What’s getting in the way?
Now, what can you do about it?