Hello

You can give your 12th board next year if you wish to but you can also give your boards this year (if you are in 12th), take a drop and prepare for Joint Entrance Exams (mains or state). As far as your boards are concerned, you just need to score around 60% for private colleges (PCM). This year there was no problem as there was no minimum marks required for JEE Mais eligibility, for 2021 jee mains you just need to pass (click https://engineering.careers360.com/articles/jee-main-eligibility-criteria )

Other than this, if you are concerned on how to prepare for your 12th boards then my advise will be to start practising the previous 15 year question papers (the pattern is the same every year). You can also get yourself arihand sample papers for the subjects. You can still do very well in boards if you study well and  not lose hope. Make a schedule and start from this very moment without5 wasting any time. All the best!