Should I retake grade 12?

It’s a shame I spend 2/3 of my grade 12 preparing for my start-up.I used to be top5 student in my grade,but this time I got a really really bad prelim result in my transcript.I want to apply for some top unis, like Stanford,Carnegie Mellon or ucb.Shoul I retake grade 12? Will that affect my application?

Well not every kid has their own start-up. We need more details. Grades, SAT scores, type of school, geographic location, etc.

What is more critical is your junior grades. It is only a month or two into senior year unless you are having a gap year.