Grades are not everything, do not feel limited by them! I am stats, rather than biostats, but I got a C in Real Analysis and low B's in multiple other math courses. My cumulative GPA is hovering around a 3.5, so my grades are far from stellar. My GRE score isn't anything spectacular either. Yet I have just accepted my place in Columbia's PhD program starting Fall 2015. In my experience, it is far more important to show them that you are driven and inspired and are the candidate who will make the most of the opportunity they have given you.