Nandana, you haven't mentioned the State you hold the domicile of. 15% of the seats of every GMC are contributed towards Central pool and they are filled through All India Counselling. For participating in All India Counselling, you do not need hold the domicile of any State in particular. But to participate in the 85% of the seats of GMC and Private Medical Colleges, you need to hold the domicile of that State. So it is important to know the domicile of the State you belong to because the cut offs are different for All India and State Counselings. Nevertheless, 500 might be a tad less score for a seat under OBC Category. Because if if you belong to OBC Category, the Category you belong to should be also listed in the Central OBC list. Or else you will be considered as General Category. And then around 500 becomes less score. So you should aim atleast 500 and above for  All India Counsellings. In 2019, the cut offs in Tamilnadu Colleges increased approximately by 75 marks on an average, If that holds the same for this year as well, 500 becomes a tad less for All India Counselling. 500 might be a good score for State Counselling in Tamilnadu but less for Kerala State Counselling.