You absolutely should not try to explain this to med schools. If I were reading your application and saw that, it would really piss me off. There is nothing worse than someone with a high GPA who complains about one B- or any variation of that story. If your overall GPA is 3.6+ then you will not be screened out. Eventually, a human will review your grades and will see that you took these courses in high school. Any credit you earned as a high school student at a major university will only be a huge positive for your application. In short, relax and just focus on finishing strong and rounding out the other aspects of your application. - Admissions to Medicine