As high as you can. You cannot predetermine the cut offs. 

They vary disastrously these years.

Best of luck. 

Try to score 550+ marks. All the best dear. 

As per last year trends, you need more than 560 marks to get into Calcutta Medical College , 

however i would ask you ti aim for 580+ for a guaranteed seat as this year competition would be a bit harder than last year(as last year there was a fiasco relating to wb board students).