Hi Silvia25,
The 16-day waiting period is the number of calendar days between appointments taken in one 'format' (re: two appointments at Test Centers or two appointments in the At-home format). Scheduling your GMAT at a Test Facility and scheduling an At-home appointment have NO impact on one another though; you could technically take one of each on the same day - although I would NOT recommend that you do that. If you score significantly lower on an Exam (in either format), then you might not want to 'rush in' too quickly to retake the GMAT (as there will likely be several aspects to Test Day that you will have to specifically train for before you will be able to score higher (and that training takes time).
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 long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) 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:
4) What is your overall goal score?
5) When are you planning to take the GMAT?
6) 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