Hello, 
You don’t need to finish all your pre-med requirements before applying to medical school, you only need to make sure to have completed them by the time you matriculate. This means that for someone applying the summer after their junior year, they have a full year of coursework before matriculation, even though when they applied they didn’t have all of the required courses finished. Medical schools may ask to make sure that you are going to complete the requirements your senior year. 
I hope this helped, let us know if you have any other questions. 
Best, 
PMH Advisor Allison