What does your grade averages in high school have to be to become a doctor, or @ least to qo to medical school?

What does your grade averages in high school have to be to become a doctor, or @ least to qo to medical school to become a doctor of some type. In my case, I want to become a Gastroentrologist. Sooo in order for me to qet into a colleqe (medical wise) what does my grades have to be on my report card in hiqh school ? I'm not the smartest, but this is my dream. I'm in 10th qrade & my GPA is 75. Is it too late to work harder this year until my senior year ? What do you think my qrade should be by the time I qraduate to qet into a colleqe for my doctors deqree. Please & thank yoooou !