GMAT Strategy

Ok, Im really struggling to make up my mind here so ill be really honest here and I need your opinion. I am targeting mainly two schools where avg gmat is 660. I also have a safety school in mind which I would not mind attending and their avg score is 640. GMAT is important for me because I am a younger applicant, recently graduated with major in liberal arts, and I do realize that my work experience is merely adequate. I do have B+ gpa and my references will be very good, I already talked to my employer about it. The thing is, I have been studying for GMAT on my own, as much as I could, since May. I have been scoring 500-520 range until mid August. Then I finally had a breakthrough, scoring 580 then 620 twice and 630. In my last two practice tests I have slipped to 580 and 570 again (MGMAT CAT's). Right now im frantically trying to figure out the reason that led to the drop in the score. The issue is that the schools I am applying too have rolling admissions cycle. In order to maximize my chances I have to apply first round and the deadline is November 15th. That means I have to take GMAT and begin working on the essays no later than October 15th. Although my target is 660+, I would be satisfied with the score of 630 or higher, as I feel that I would still have a shot at my first choice schools with that score. If you were standing in my shoes, do you think you would go ahead and register for the 12th of October test date or would you let the deadline pass and target next year admissions? Is it realistically possible to go from 580 to at least 630 in a month? I really need a piece of advice here...