Hi khushalkhans,
To start, you have given yourself lots of potential study time before a December Test Date - which is great! When it comes to scheduling an Official Test Date (whether at a Test Center or through the At-home option), you do not necessarily need a lot of lead-time - meaning that you could potentially schedule your Exam for tomorrow as long as a 'slot' was available and there were no issues with how you intended to pay for your Exam. With a Test Center, you do have to account for the fact that each facility has a limited number of computers (thus, it has a limited number of potential Test-Takers who could take their respective Exams at any given day or time. As such, to make sure that you take your Official GMAT at whatever time is best for YOU, it would probably be a good idea to book your appointment well in advance of when you plan to take the Exam.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How many hours do you typically study each week?
2) On what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
3) What is your overall goal score?
4) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich
Contact Rich at: Rich.C@empowergmat.com