Karen,
Don't think of it as being how low your scores can be. Think about if you have done your best. If you have, then proceed with your dreams. It's not easy, (it was defienently a challenge for me) but your application is more than MCAT scores and a GPA. Of course those will get you in the door (by means of a secondary) usually. But your extra-curricular activities (research, work, community involvement, volunteering, extra classes, EMT, etc.) are VITAL. Think of yourself as an admissions commitee member and imagine if you would accept yourself. (Don't be easy on yourself either.) If you think you are competitive, I suggest that you look up the post regarding the MCAT and GPA averages of the entering class as a reference. Then go for it. If you truly want to do it don't give up! If for some reason you don't get in, improve your application. If you get the average or somewhere near the average for the MCAT, ask the admissions commitee if you should retake the MCAT over.
Remember what a pain the MCAT was. Studying for it may take time from all your other extracurricular activities. Try and balance you medical experience. Look at your application, if you see anything lacking think of ways you can improve it. The best thing is to talk to people that have got into school. It will give the strength to go on.
Best of luck,
Duke