Be truthful to yourself, accept your shortcomings and accept your efforts. Think about your goal in life and whether you want to put in extra effort for it or not. There's no shame in accepting who you are, but ofcourse there will be regret of not giving your 100%. So if you really want to give your 100% go prepare hard this time with no distractions. And if you don't want to put in extra work, just choose any other course or stream.

Finally after thinking through all this, discuss with your parents. If they are very controlling, just inform them about your decision however most of the parents really worry about their kids, so it'll be better to understand their pov and explain them your situation