To help remember your effort and progress – to then help build confidence for the viva – keep records of what you do and what happens during your PhD.
You don’t have to have a minute-by-minute journal of what you do: perhaps start a tally and for each day you show up to do something for your PhD, make a mark. Each time you finish a task, make a mark. Whenever you do something new, make a mark. Whenever you feel you’ve learned something, make a mark. And so on.
Whatever challenges you face, whatever gets in the way, – and particularly whatever makes you feel like you’re not going as far or as fast as you might want to – perhaps all you need is simply to show yourself, with a few marks, that you really are making progress.
You really are good enough.