Well, the average matriculant GPA is around a 3.5. Any A's will bring you above that and any B's will bring you below that. So basically, B's are bad. If you are having difficulty in school right now because of other obligations, I would suggest putting it off until you're ready. Adcomms tend to be notoriously unsympathetic about other obligations and you'll have a very hard time getting into med school with 3.0ish GPA. It's not impossible, but it's difficult.