I have 90% marks in class 10 and 12 but 59% in graduation from Calcutta university. What are my chances of getting a good b school ?

You already have 59% in graduation so now you need to prepare for entrance exams give entrance exams like CAT and CMAT and score good to get a good college You should start preparing for entrance exams now onwards since you are graduate

Good B school have entrances and to be eligible for it, you need 50 % in graduation. So prepare well get a good rank and apply.