Advice on Retaking SCH4U

I have an 83 in grade 12 chemistry because of my IB exam. I was predicted higher, so I believe if I retake the course, I would get at least low 90s. However, summer school registration is closed in Ontario, so I would like to know if it's a good idea to take a course from a private school for around $ 500. Do universities view it negatively? Like I want to get into top health sci and like life sci programs in Ontario, but like with that 83 my average is 92.