Hi Adeela,

You can most definitely give your class XII examination in 2020 in spite of having such a long gap between your 11th and 12th as a private candidate only as almost no good school would like to enroll you irrespective of how academic you are due to the fact that you have a long intermediate gap.

Thus I would suggest that you do your class XII from National Institute of Open Schooling(NIOS) which is a government recognized board and then pursue your graduation and higher  studies.

BEST WISHES!