Have you done everything you could for your research and thesis? It’s almost impossible!
Have you done enough for your research and thesis? Probably, since most candidates do!
It helps to define “enough” before you try to decide if you’ve achieved it.
Similarly, you can’t do everything in preparation for your viva, but you can do enough. Figure out where you have gaps, where you need support, where others can help you, then work your way to being ready. Decide in advance on what you need to do before you get to work.
You can’t do everything, you can do enough.