What did you not know at the start of your PhD that you know now?
What could you not do at the start of your PhD that you can do now?
You had to start somewhere. There had to be gaps you needed to bridge, things you needed to discover.
Reflecting on your progress should help with confidence for the viva, because you appreciate just how much you must have developed to get the work of your PhD done. You did it, and you must be good enough.
Still, when you look back it can raise the odd worried thought. Perhaps something is unfinished. Perhaps there are gaps in your knowledge. Perhaps there was more to do.
If you have unanswered questions or unpolished skills, it won’t be because you’re lazy. A PhD is long, but doesn’t give enough time to learn everything or become proficient in every method. Perfection is not the standard required for you, your thesis or your viva.
You did the work to get you this far, and you must be talented, you must be good enough. Look back to the start of your PhD to get a sense of just how far you have come.