The same thing happened to me when I was 16! My doctor was really just a big jerk who always made me feel embarrassed, so my anxiety
level was always through the roof when I was in his office. One time he checked my BP and it was extremely high, and based on that one time alone he wrote me a prescription for an anti-hypertensive (which lowers BP considerably). Considering the fact that I had normal BP all the rest of the time, this medication could have seriously hurt me if I had taken it. From that time on I have had fear and anxiety when I think about going to a doctor, which peaks while I'm in the office.
If your doctor is nice and a rational person, you should make another appt with her and explain that you have a bit of a problem with anxiety in the doctor's office. Explain that it's a general anxiety and not a fear of her in particular. She will almost certainly understand and appreciate your being honest with her.
If your fear is very intense and uncontrollable, you may have 'iatrophobia' which is essentially a fear of doctors. Check out http://iatrophobia.com/phobia.htm . If it's not that severe, don't feel bad because it's more common than you think. Doctors and their offices can be intimidating! If you only have a problem with this doctor in particular, you should consider looking for a different one.