You can’t be perfect: you can be good. You can know enough and do enough to be good enough for your PhD. You can show enough in your thesis and in your viva to convince your examiners that you’re good.
By submission you must be good. I think for many candidates there is a belief gap – they don’t believe that they have become good enough. Some are not sure that they ever will be good enough.
You can’t simply wish to feel differently. Instead, reflect on what you’ve done to get this far. Analyse and list all of your achievements, big and small, that have lead you to submission and to viva preparation. Reflect on your talents and really see that you’ve done enough.
Know what you are good at – and know that you are good.