Placement worry after b.tech in cs .shall i repeat in 2019 or improve 12 board to make it a 4 yr gap as class12%-55% in 2018 and class10%-75% in 2015 .1 yr xtra in repeating class 11.
I was bad in studies but now geared up to excel in my life with motivated soul inside me
I'd say do not repeat. You will simply be wasting precious time. Instead, try to get admission into the branch of your choice and work your ass off to get good percentage in engineering exams - throughout the course.
In addition, try to acquire all the skills you can that are related to your branch. If your choice is CS, try and become master at a programming language, participate in hackathons and build an impressive resume.
Be an awesome programmer or computer engineer that companies would die to hire. If you do all that, do not forget to apply to a position at CrazyEngineers. We'll hire you, if you're awesome. ?