Yes, you can file RTI for Copy of your Answer Sheet from Central Board of Secondary Education (CBSE).
Central Board of Secondary Education (CBSE) is a national level board of education in India for public and private schools, controlled and managed by Union Government of India. CBSE comes under Department of School Education, Ministry of Human Resource Development. CBSE is a "Public Authority" as per Section 2 (h) of the RTI Act 2005.
You can file RTI for Certified Copy of your Answer / OMR Sheet under Section 2 (j) of the Act by addressing the same to the designated "Public Information Officer (PIO)" of the concerned Regional Offices / Head Office. You can either file the Application Online or Offline mode by paying the prescribed fee.
To know more about the procedure to file RTI Applications Online for Central Govt. Departments, please refer https://onlinerti.com/how-to-file-rti-online-for-center