Hi Sayan,

Students are admitted to IITs on the basis of their preparatory rank only if seats are left in normal rounds of counseling. Only 20-30 students are admitted every year because almost all the seats get full. At your rank, chances of getting admitted to the preparatory program are very very less. If you're so much keen to join IITs, I would suggest you to take a year drop and prepare for JEE again.

All the best