Can i get into university?

i want to go to the university of mcmaster in hamilton ontario. i want to enter the health sciences program and the grade average is a MINIMUM of 90..it is a very competitive program to get into and i really want to do this. the only problem is i have been slacking this semester and i ended biology with a 72, chemistry with a 70, and advanced functions with a 74...i am in grade 11 though and i KNOW if i get it together i can get a 90 average next year( i achieved my current marks by never having done homework/studying for tests/exams)...so my question is..will universities look at my mark from grade 11 and is it important even if i have much higher grades next year? is it a better option to stay for 5th year and take these courses over again?(with this i could spend extra time earning volunteer hours(which will help me get into the program), and i could take any courses that i want a higher mark in over again? what do you think? i would GREATLY appreciate advice from someone in a similar situation or with past experience of this.