Grad from LECOM-B here (2016)!
Probably the most important aspect of success in PBL is your efficiency of studying. I struggled at first as I was putting in a lot of time looking at the material, but I did not have a great structure to digest and re-review what I was seeing. PBL is amazing as it lets every individual study how they would prefer, but you should try to have a good idea of what works best for you going in.
For me, just reading a chapter over and over and over was useless. I was the type of person that needed multiple sources on the same topics so I could add variety and interest into what I was doing. Flashcards, Q-Banks, Videos, Review books, and the material are all options. And once you think you know a chapter...find a way to quiz yourself! Talk to your close friends, use a Q-bank, do anything to expose where you are strong and where you aren't.
Finally, realize that you have already made it into the 0.1% of people that grew up wanting to become a medical professional. It is ok to be in the middle of your class. It is even ok to be in the bottom 1/3rd. Don't be hard on yourself, and if you feel you are falling behind ASK FOR HELP!