Yes, you can apply RTI to obtain Copies of your Answer Sheets from Punjab Public Service Commission (PPSC).
PPSC was established under the Government of India Act, 1935 and presently functions in accordance with the ambit of Punjab Public Service Commission Ordinance, 1978 and Punjab Public Service Commission (Functions) Rules, 1979. PPSC is a Government Agency responsible for hiring and administering the Provincial Civil Services and Management Services in Punjab. Hence, PPSC is a "Public Authority" as per Section 2 (h) of the RTI Act 2005 and comes under its ambit.
You can file RTI to obtain Certified Copies of your Answer / OMR Sheets under Section 2 (j) of the RTI Act from PPSC by addressing the same to the designated "Public Information Officer (PIO)" through Registered Post and by paying the prescribed fee. You should attach a Copy of your Admit Card and mention your Roll No., Registration No., Name of the Exam clearly in the Application along with a Govt. Photo ID (Aadhaar Card / PAN Card/ Voter's Card, etc.) of yours as per Punjab RTI Rules.
To know more about the procedure to file RTI Applications for Answer / OMR Sheets, please refer https://onlinerti.com/how-to-file-rti-online-for-exam
To know more about the procedure to file RTI in Departments of Punjab State, please https://onlinerti.com/how-to-file-rti-online-for-punjab