Hi! I would highly recommend going through the syllabus and going through the mark-scheme; highlight what you would need to do in order to hit the top bands, and make sure that whatever you do is geared towards achieving those top marks based on that. Look at the weightings of each component, and make sure that you put in extra emphasis/more effort towards the components that cost the most marks. Based on the weighting, the essay is actually not your utmost priority. Hence, make sure that you note down all the advice received from your supervisor in a document (this will help you so much in your reflection, which is weighted extremely highly), make sure your progress log is as detailed as possible (complete it as you go), and reflect on your pitfalls as well. It is inevitable to meet problems throughout your project, and they want to see how you got through it and improved.
If it makes you feel better, my EPQ essay wasn't that great, but I would say that I was predicted an A* (I'm in Year 13 currently and the results aren't out yet) because I went through the process I mentioned above. Your final product doesn't have to be perfect by any means in order to get a good grade.
Good luck, you can do it!