Worried about whether or not you’ve done enough prep? Worried if you find a reference after submission that seems like it would be a good addition to your thesis? Worried that there’s something else that you just have to do before the viva?
Whenever I get stressed out and think I need to read more or do more, I remember a little line from Ecclesiastes 12:12. Probably 2500 years old and still relevant:
“…There is no end to the writing of books, and too much study will wear you out.”
You could read one more paper. You could check one more detail. Make one more note. But do you really need to?
At some point you just have to stop. Weigh it against everything else you’ve done, and you’ll find the right point.
Don’t exhaust yourself just because you’ve found one more thing you could do.