Don't sweat it. What is done is done. I know many MD/PhD students who don't do well on Step 1... go figure since we are supposed to be good at the "basic sciences"... My theory is we are over analytical people and taking a test that has multiple "correct" answers we can talk ourselves into or out of the right answer. I did less than stellar and rebounded with a score in the 250s. I bought crush step 2 before going back to med school and read it before going back. Not to improve my step 2 score but just to remind me about medicine. Going back into 3rd year of med school is very hard, it is an entirely different mentality. Study hard for shelf exams, do lots of practice questions and take step 2 early (as close to your shelf exams as possible). USMLE world is great and I also agree to buy the 1 year subscription during 3rd year, it will help your step 2 score and shelf exams. Also I really liked USMLE Step 2 Secrets. That being said, spend your PhD years applying for grants, writing manuscripts, and finishing your PhD work in time NOT studying for Step 2. If you want to stay up to date consider tutoring for a little extra money AND the bonus of staying current.