So Im feeling a bit like a failure...?

I want to be a doctor when I grow up, but Im not that smart. I took Bio and did really well on all the exams (i got A's on all of them), and ended up with B+. I was really upset. Right now I'm in anatomy. I almost threw up in the labrotory when we were studying the cadavers and ever since we started studying them my quiz grades have dropped. I took a midterm today, and I studied my off and only got 55%. My friend whos studying to become a nurse, didn't study at all got an 85%. So I kind of put doctor behind me I'm thinking about being a occupational therapist. Im just really worried about the future job market and being successful.