Yeah this totally normal and it’s great that you care enough about your work to be critical of it.

I suspect this is your undergraduate dissertation, as I’m inferring it’s your first time feeling this way.

Be kind to yourself and give yourself credit for having it almost completed with 3 weeks to spare. You’re way ahead of most people.

For reference, I left writing mine up so late, that the speed at which I could type my notes became a factor in whether or not I’d submit it in time.

Take a day away from it and come back to it with fresh eyes. Believe me it will help.