Replying to Critical Essay Help

Sparknotes at bottom

Alright well I'm doing a 1st year university critial/analytical essay on Benedict Anderson's Imagined Communities For those who don't know what it is, its a book analyzing the rise of, evolution and effects of nationalism in its various forms. The task is to analyze the author's arguments for clarity, plausibility strengths and weaknesses. Sounded easy enough. However I spent 6 hours writing today and ended up with 7 pages and I hadn't gotten through 2 of the book's 11 chapters. The assigned essay length is  12 pages. The things due Wednesday and I'm thinking well fuck there goes my weekend. I'm obviosuly writing FAR more than I should be however I can't find a suitable balance between summarizing the author's aruments and then detailing my critique. His points are so logically structured built one on top of the other other that i don't know what to exclude without damaging the integrity of my review. How should I keep this shorter NS? Which points should I detail and then argue?

Sparknotes: Im writing a critcal essay analyzing and critiquing the arguments presented in a book about nationalism How do i know which arguments to pick and choose as not to go crazy in-depth and make the thing too long?