Hi Adrija, 

If you score above 75% that is 540, there will be a good chance of you getting into medical college kolkata as an sc candidate. however, you can never be sure until the results are out and you know your state and category rank. it is very hard to tell you a minimum score as this varies every year. if your category rank is below 100 there will be a high chance of you getting in to medical college, kolkata. 

Wait for the results and hope for the best.