I think I have go to the hospital
If you're trying to say you may need to physically be at the hospital. You would say "I think I have to go to the hospital."
To go is the action.
I think I have got to the hospital
This sounds like you're saying you think you have arrived at the hospital. In any case, the correct way to say that would be "I think I have gotten to the hospital." However, "gotten" is an American word.