Hi eltonj,
The pool of questions that comes with each GMAT CAT is limited - so retaking any of those CATs will lead to a certain number of repeat questions. As such, those 'retakes' will NOT provide a realistic score result. You can still use those CATs repeatedly for general practice, but if your goal is to receive a realistic score result, then only the first attempt at each will give you that result (assuming that you're seeing a full set of *new* questions).
Thankfully, there are enough realistic CATs on the market that you can continue to practice.
How long have you been studying?
What resources have you been using?
How have you been scoring on your CATs?
What is your score goal?
GMAT assassins aren't born, they're made,
Rich