Your prep will be imperfect. Getting ready for the viva, there’s no way to account for every bit of information you might need. You can’t anticipate every question you could conceivably be asked by your examiners.
Your prep is built on layers of imperfection too. Your research won’t be perfect. Your skills will not all be at their absolute peak. There will always be ways to make your thesis better.
In all of these things, you don’t need perfection. Your prep doesn’t need to be perfect, it just needs to make you ready. It needs to make you good enough.
Your prep, while imperfect, can help make you ready for anything you’ll find in your viva.