It’s totally fine, 11th class marks was not a correct representation of your 12th marks. It’s totally different. But If you scored 83% marks in 11th (PCM) it’s highly probably you may get above 95% marks in class 12th.
But wait a minute….
Why you wanna focus on class 12%. Yeah we know society praise you for few days. But then what? Your more focus should be on JEE mains, If you wanna study in India. And if abroad your eassy and other things like SAT.
But even you don’t interested in JEE mains, Even then your focus should be on some Entrance exam. University of delhi from 2022 onwards takes admission on the basis of entrance, not on marks. Now the Reliviance on board marks, on university admission is very few or negligible. As they don’t represent real you.
But if you, like all are concerned of your performance, you are on right track. I wish you scored good marks in your examination.