Responses At The Viva
You don’t need perfect answers at your viva. You don’t need perfect responses.
You need to be prepared to respond well to your examiners but that doesn’t mean that you need to have “prepared responses”. Your examiners want to have a good conversation with you about your work, the process that lead to it and your capability as a researcher.
They don’t want you to read from a script and they don’t expect that you will have practised every possible permutation of question that they might ask.
Read your thesis. Write some summaries. Rehearse a bit.
You don’t need to be perfect. You need to be prepared.