Need some Advice, Hopefully someone can help.

I have a Quick Question, il make it short and sweet.

i plan and want to be a Surgeon. My Highschool marks are bad

If i take all Collage courses in HS (Instead of University) will i still be able to go to Uni?

If not, Should i go back a Year and take Gr.11 Uni's so i can take the 12's? or is it a waste of time?

Need some Advice, Hopefully someone can help.