Essay marked unfairly

I just got back one of my essays, and it is the only one this term that didn't get a First -- it's a 2.2 :/ The feedback that I got is that the argument is very good, but that I didn't rely enough on the core textbook, hence the 'engagement with literature' mark is extremely low. The course is not different than any other politics courses that I am doing, and it is meant to be marked using the same criteria as the rest of the politics essays, but the feedback contradicts university guidelines. I am really not sure what to do now, because that grade is really important considering what I want to do with it, but I don't want to go to my lecturer, throw the university regulations in his face and say that he's wrong. (Also, another lecturer gave the essay a mid to upper 2.1 - it got marked down later.)

Any advice?