There are so many things PhD candidates could be unsure of…
I’m not sure what the rules are for examiners, who can and can’t be one.
I’m not sure how long I could get to do my corrections.
I’m not sure what to do to feel ready.
I’m not sure how to get rid of my doubts.
I’m not sure if my supervisor will run a mock viva.
These uncertainties drift around. It’s not unexpected that you could be unsure of something related to the viva.
The solution, thankfully, is straight-forward. Find out. Ask. Get sure.