I don't want to become a doctor! Help please.

Hello everyone. I just signed up in this website to get some help and advice.
I have completed my a levels recently and got A* in biology and chemistry, A in physics, B in Mathematics. I love maths and physics and chemistry too, but I just don't have any interest in biology or becoming a doctor.

After my A level results in August, I applied for a top medical university in my country and got first position in the entry test (in January) in my province, and got selected. My father suggested me to be a doctor and at that time I accepted his suggestion, but now I feel that my mind is changing. In fact I never wanted to be a doctor. I always wanted to be a mechanical engineer.

The university classes will began in November and that will be 2 months from now. I just wanted to ask if it's possible to prepare again and apply for an engineering university. I don't know if it's the right choice. I think I can get admission in a good engineering university, but the problem is that I may end up wasting a complete year, already I have wasted alot of time. I will have to restudy again all the material. I will also have to give up the medical college, and I don't think I could convince my father.

Besides, I had suffered from OCD through out my life and I am very afraid of diseases and making a mistake as a surgeon and losing a life or contracting a disease myself. I am not good at taking quick decisions or in practical work or at rote memorization. I am not a doctor material. But is it possible that even if have to become a doctor I could just adopt. Is there any field in medicine that involves math and doesn't involve surgery or treating patients. I am thinking about research but I think there is not much salary in it. I will be very thankful for any advice. Thanks a lot!

Thanks pitseleh for replying. I need some more advice please. I am planning it like this. I go to medical college and attend the first semester. I will get 2 months(June and July) vacation after that. Perhaps I can prepare for the entry test for engineering university in the 2 months(it's just revision) and give the test in August. If I fail I will return to medical college but it's worth a try. I would be indeed grateful for any advice or opinion. Thanks a lot.