When the date is in the diary your viva is going to happen whether you’re ready or not.
Don’t agonise over the date. Don’t fret about what might happen or what your examiners might ask.
Instead do the work. Do the work that’s needed to get ready.
The work will help steer you away from concern and lead you towards confidence. Preparing for the viva is a practical path and not a long journey – certainly not compared to your PhD as a whole.
Your viva is going to happen, ready or not. Choose to be ready.