I'll start by saying do not feel discouraged or freaked out. This is a tough exam, but it can be beaten. Also, by "traditional" models, you should be using purely AAMC material during the final month of preparation.
Assess your weaknesses by going through the exam. Gauge why you missed a question. Fatigue, lack of knowledge, stupid mistakes. Gauge questions you got right. Did you guess, or did you actually know the material or will able to justify it based off of the passage? Did you feel rushed for time? Each question in itself contains a "Seed" of sorts which is a lesson on how to improve yourself for next time. (Adaption of a quote.)
Next question to ask yourself is what is your target score? 501 can be easily improved, but time is of the essence. You need to make some time to take the AAMC exams as that will be the true gauge of how comfortable you are with their material in their format. If your goal is 510+ maybe 3 weeks may not be enough. That is your own judgment call to make. The average matriculant to MD was 511, I believe. (Or somewhere in that vicinity) Couldn't tell you DO.
The final question is, should you choose not to change the date of your exam and feel comfortable with your practice scores... are you considering the option of a retake?
