Hey Poonam.

Yes, you can pursue a three year LLb course if you have already completed any graduation degree like Bsc. As the eligibility criteria for the colleges of Three year LLB do not have any upper age limit, you'll be eligible to take admission in the course even if you've completed Bsc in 2003. You would require a minimum aggregate of atleast 45-55% marks in graduation degree to be eligible depending on the college you're seeking admission in. Here is a list of law entrances for 3 year LLB course -  

DU LLB - Delhi University  

MH CET- GLC mumbai, ILS Pune and other colleges in Maharashtra

SLAT- Symbiosis Law school

PU LLB- Panjab University, Chandigarh    

LSAT- Jindal global Law school, IIT Kharagpur and other private law colleges

BHU LLB- Banaras Hindu University 

BVP LLB- Bharatiya Vidyapeeth

TS LAWCET Etc

Best of luck!