@StupendouslyStupid
Please please go & talk further with your supervisor. They are best placed to advise you.
And you've had loads of excellent practical advice here.
If your supervisor is happy with your approach, then focus on that. I am giving you my own experience on research, both my own and in my professional field where I work with many MA students and researchers.
But I can't know your specific situation. If you agreed an approach with your supervisor and you've done that, then great!
If it's only the actual writing part, then that's doable and you need to stop worrying about it not being good enough. It will be.
We can all use that fear not to write a word - but you have to move on. It's actually another form of procrastination.
Here's a plan.
Tomorrow, up early, decent breakfast, then walk / swim / sit in garden - get out in some form.
Take 45 mins to capture in any form your main argument, your key themes, big points arising from your research, possible conclusions.
Take a break.
Come back and write down your worries, what's really stopping you, and come up with a solution for each.
Find one key part of your research and write it up.
You must have an abstract? Your original proposal? Your lit review? These are all parts of your 10,000 words so put them in.
Then take one key point or theme, set a timer and write about it.
Then decide next step for Monday morning: supervisor, extension being key.