My name is Chantal and I completed the Pre-Health Science program at Fanshawe College last year, so I can help you with any questions or concerns you may have (I was where you were once, wondering about low grades and all)!
I believe that for the Pre-Health program, you can apply with U or C level courses (University or College). I, myself, has really bad marks in most of my grade 12 classes, and many final marks were even in the 60's.... so I was worried when I was thinking of applying to the program. I spoke to an academic advisor from the college, and she told me to apply for the "January intake" instead of the September start date because not as many students apply for January, and that would increase my chances of getting in - and it did since I was accepted. I would suggest you apply as well for the January start date.
I also want to tell you that even though some of my grade 12 marks were in the 60's and 70's, my English was very good and my final math mark was a 98% (This was my second time doing math, this mark was from some academic upgrading I had done). So, as long as you have your english and a good math, I think you have a good chance of getting in!
I'm SO glad I took the pre-heath program at Fanshawe; it was really helpful and thanks to working hard, I recently got accepted to the MRT program, as well the BScN Nursing at Western. I couldn't have gotten in either program without Pre-Health.
So, don't give up your dream of getting into Pre-Health.. even though you don't have the best grades, you can definitely still get in; I did, and so can you! Upgrading a few courses over the summer and/or fall can help you too. Do what you have to do to increase your chances. You have lots of time - I'm 25 years old.. it took me a while to get to this point, but I'm finally on my way to being a nurse or MRT!
Let me know if you have any other questions about Pre-Health or anything related! I'd love to help.