When I was a freshman, I started heading towards a C- in an important math class (I was an aspiring physics major). At the time, I was crushed, and spent all my time thinking how bad my life would be with a C-, instead of working to bring that grade up: I never did. When it came time to start thinking about getting the ball rolling on declaring a major, I was flat out rejected from physics, as the administration pointed to my poor performance in math (and probably a fair rejection at that!).
What was so weird was that I sailed through math in high school, and had never had any trouble anywhere else. I remember having incredible feelings of self-doubt, and as I thought math was my one thing, I let my poor performance spiral me into depression. I almost transferred out of my dream school, figuring that it was a mistake for me to think I could cut it.
As it turned out, I wasn't bad at math, but I was bad at dealing with setbacks. As I recall now, I began at the mean, and doubted myself to a D on the next two exams. It was all in the attitude, and I learned a big lesson the hard way: don't take it personally.
Now what you probably wanted to hear: I made it. After an attitude readjustment, I rediscovered my talents that were always there. Instead of focusing on setbacks, I focused on what went right. My next semester back, I took an even harder series of courses in physics and math, because this time, I had something to prove to me and the school. I ended up with a 4.2 that semester, my best over all 4 years. When I went to reapply for my major, they looked at my freshman year grades, chuckled, and said "welcome aboard!" I just graduated with a physics major and a 3.9, and today have great offers from top med schools. I actually wrote a secondary essay on the lessons I learned, and as evidenced by my acceptance + mega scholarship, it worked!
The point is that, yes, a C- is bad, but only if it continues, and there is NO reason why it has to. Figure out what went wrong, take a deep breath, and get back on the horse. This is so standard for freshman, who get thrown in with people with all different types of education and training. I don't know what your situation is, and it is probably different than mine. But for any freshman, if someone tells you that you can't do something, or that med school is out of reach, it's just way, way too early to tell! Fixing the problem will make this a non-issue in admissions (I sometimes think I am helped by my story), but you have to fix the problem! Good luck and get back to studying!
PS Aside from my little story about attitude, as a TA of 3 years, I can almost guarantee you that your best bet is to do problems again, and again, and again. When you run out, redo past ones. Reading the book will get you 10% of the way there. Problems: 90%