You might find it helpful to plan your assignment, identifying themes that you intend to cover. There are many ways to organise your thoughts, below are two suggestions.
Visual plan
Below is an example plan from Anna Barker - it shows you how to divide your topic into sections. As you find some research that fits into a specific section, colour-code it, so you can see immediately which parts belong together. Is there too much in one section? Is there not enough in another? Will you need to do more research on that section perhaps? Colour coding makes this easier to see. If only have 1 or 2 pieces of research for one section, you'll need to look for more research.

Linear plan
If the visual plan doesn't work for you, here's another way of planning.

Dividing the word count enables you to give all the criteria equal weight. You could include a 'Key points' column to remind you how this theme fits within the overall argument of your assignment. You could use the 'Notes' column to provide a link to key resources, or to give yourself 'to do' instructions, or to comment on how far you are with your writing.