Am I failing my dissertation?

You really need to discuss this with someone in your department. Where is your adviser in all of this? That's the person you should be talking to about this and who should be giving your more guidance on what you need to do to improve. This one thing only counts for 20% of your grade, so unless you do really poorly on the rest of the sections I think you can salvage the grade. You might not walk out with a very high grade, but I see no reason why you couldn't p.