We both know that this looks bad, you can't and will not retake it for a third time. Instead what you will do is take the Functions/Calculus course(s) . Reason being is should you get into RMC you will do math even if you are in Poli-Sci. Might as well see it once before hand when all you need to worry about is school. Furthermore if you don't get in to RMC not having calc is a huge problem in university if you want to switch majors out of poli-sci you pretty much need calc. What you are going to do is take it, study hard go to your math help session or math club at lunch and ensure that you do better than your 65 in grade 11. Ideally low 80s. (I failed functions in HS, re took it and got a 83, there is no way that you can't do that as well). Can't understand your teacher? Don't worry https://www.khanacademy.org/ has your back.
Good if you are taking a victory lap take the G 12 courses as well. The only caveat with the 5th year is towards the end of the final semester once I got declined from RMC and was going into a program that didn't need my bio/chem courses my GAFF (give a frig factor) went a lot lower. Not saying that this will happen to you but this happened to
most students who came back for the final semester,
if they even finished the final semester. You have got to keep your self focused, because you never know when you will need the credits. (Like when you try to switch into engineering and get told no :
).
It doesn't necessarily need to be physical, what about things like chess, debate? If you started now you could get 2 years of activities in. But by all means do what you can for next year.
You could also do some volunteering, but try to do something longer term and with a bigger impact for yourself.
No one can tell you your probability, it depends on you and how competitive the other applicants are applying to your given trades. Good on you for trying to to do this now, instead of the year that you are applying.
Cheers
