Hello Buddy! Hope you're doing good.

As you're not alloted a rank in JEE Advanced Rank List. The vacant seats are reserved for SC, ST and PwD candidates, which don't get filled in the counselling will be allotted to the candidates of respective categories for admission to a preparatory course. So with your prep. rank, you might get a seat in IIT which may varies depends on the number of vacant seats available and the number of prep. rank before your rank applied for IITs. Further if there's seat available then  you will get a seat. Hope this will help you.

ALL THE BEST! WORK HARD !!