Do what you can to try to fix whatever you can for the rest of the semester. If you think it's beyond help, take a W. Keep in mind that when you apply to dental school, you only need to have 2/3 of the classes completed-- should you have to retake it in the summer. Some schools also have sister schools that offer classes during the off semester, so you may also want to look into that. Best of luck; remember, for the most part, everyone is at the same level intellectually-- it's all a function of how hard you work. Also keep in the mind that you should should be working SMART, not just necessarily HARD. Good luck.