I have fond memories of my PhD, but also a background feeling that it could have been so much more than it was.
I could have been more pro-active; I realised quite late that I could set my own directions and goals. I could have achieved more. I spent a long time following dead ends and trying to force ideas and results to work, without stopping to see what the real underlying problems were with my research.
Maybe I could have worked better had I realised what my own underlying problems were.
Like me, you’re not perfect. Your research and thesis won’t be perfect. But focussing on the imperfections in advance of your viva probably won’t help you to get ready. Instead, acknowledge the things that could be better, make a note of anything that might need special attention and then start your prep centred on the things that you do well.
Start with your successes, your results, your talent, and use that to build on. Not everything can be amazing when you look back on your PhD, but hopefully there’s enough there to help you feel good for your viva.