When it comes to viva prep there are lots of ways you could try to prepare.
You could read your thesis once and leave it at that.
You could read and re-read your thesis to try to remember everything.
You could obsess and try to make everything perfect.
You could do nothing and shrug your shoulders, saying “What happens, happens!”
You could worry, and hope that nothing too bad happens.
…you could learn what to expect, reasonably; you could know your thesis is not perfect, and that’s OK; you could do a little prep, making sure you have a good general awareness of your thesis and research and time to rehearse in some way; you could work on building your confidence, so that you go to your viva as sure as you can be that you will succeed.
The last approach is my favourite of course. It’s less simple than the others, but easier to do.
How are you working your way to being prepared?