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 will get a seat in IIT but the branch may varies which depends on the number of vacant seats available. If there's seat available in CSE then sure you will get a seat. Hope this will help you.

ALL THE BEST! WORK HARD !!