Do make sure retaking those "C" classes will not hurt your MCAT study time...i think this test can make a major difference. Like
@heybubba said.. there are people with lower GPA that get into MD schools. Just make sure you do well in your re-takes and on the exam. Retaking the classes isn't a bad idea.
But you have done a post-bacc program already isnt that "upper level bio courses?" OR didn't it include some upper level classes like cell biology, neurosciences ...etc so why would you want to take them again the fall?