Hi ksuraj517,
Currently, you can take the At-home GMAT just ONCE (regardless of whether you accept your Score or not). This one attempt does NOT impact the number of times that you can take the GMAT at a Test Center (nor WHEN you can schedule those attempts). Under current rules, you can take the Official GMAT up to 8 times at a Test Center (but you have to wait 16 days between attempts and you can take the GMAT no more than 5 times in a 12-month period).
You could potentially schedule an At-home GMAT and a Test Center GMAT on back-to-back days, but I would NOT recommend that you do that. The process of taking a FULL-LENGTH Test (whether the Official GMAT or a practice CAT) requires a significant amount of effort and energy - and takes time to 'recover' from. If you were planning to separate your two Test Dates by approximately 17 days, then that would probably be a good idea. That having been said, if you score well-below your Score Goal on your first attempt, then you might want to push back the date of your second attempt (so that you can put more time into honing the necessary skills to score higher).
GMAT assassins aren't born, they're made,
Rich