If any degree certificate or consolidated mark sheet is lost, it is better to lodge an FIR. Because, if it has been misused for taking a bank loan or a getting a government job at some point of time, then you will not be troubled later by the authorities when the fraud comes to light or is investigated.
In your case it is almost three years since you lost the certificate, do you have a genuine reason for the delay? This may be asked by the police/school or the board.
Many SSLC boards allow online application or downloads. You need to have your registration number, hall ticket, date and year of the exams, Identity proof and money or DD for the requisite fees.
The procedure varies slightly from state to state.
1. Letter request/Prescribed application form duly filled and signed by the Head of the institution
2. Reference number, Hall ticket, Register number etc
3.Submit with the fees to the board
4. The board would check your details, their record and then a duplicate marks card will be sent to the secretary of the state SSLC board to be signed.
5. Then it would be despatched by speed post to the institution where you studied.
6. It takes around 1 month to get the duplicate mark sheet. In Karnataka, there is a speedy process if you pay extra money
7. It would be better if you apply in duplicate or triplicate so that you have 1-2 spare mark sheet in case you lose one. Please keep the acknowledgment receipt handy from the board because it would be useful there is a delay or misplaced post.