I’d recommend taking a diagnostic exam before you dive into your MCAT studying no matter how many pre-med classes you have left. It is essential to gain a clear idea as to where you are starting from. If your exam date is still one year or more away, instead of using the AAMC practice problems (access only lasts about 1 year), I’d recommend using one of the other free diagnostic exams available out there (such as the Free NextStep Half-length).