Hello aspirant!
Hope you are doing good!

You haven't mentioned your BOARD- is it CBSE/ ICSE or state board.
Assuming that it is CBSE, You'll be happy to know that CBSE has started the application process for class 12th optional exam for those who wish to improve their marks. The private students will have to apply online at the official website of CBSE- cbse.nic.in.

Candidates of class 12th whose result has been declared, if they are not satisfied with their exam can appear for optional exam.
They can improve their performance through it. Such students will be issued a consolidated mark sheet.
https://cbse.nic.in/newsite/private/index.html