Hello aspirant, as you mentioned that your preparatory rank is 821. And you belong to SC CATEGORY. To know if you have got a chance to get into IIT or not you need to understand what this rank means. Mentioned below are all the details you need to know -

There is another rank which is given, apart from CRL, called as JEE Advanced Preparatory Rank.Firstly, This doesn’t mean a rank in JEE Advanced. You’re not alloted a rank in JEE Advanced Rank List. For example, if your JEE Advanced Preparatory Rank is 150, then it will be written as 150-P. It is completely different from CRL and it has a different meaning also. Let's know more about it.

The vacant seats reserved for SC, ST and PwD candidates will be allotted to the candidates of respective categories for admission to a preparatory course of one-year duration on the basis of relaxed admission criteria. Admission is given to the candidates in the preparatory course provided

The seats reserved for the respective category are vacant and

Candidates have not accepted a seat in the preparatory course earlier.

Major Important Points Regarding Preparatory Courses

IITs (not all) runs preparatory courses of one year duration for SC, ST and PwD candidates intended to prepare them to pursue the academic program (for session 2020–21) to which they have been allocated.

At the end of this course, candidates are declared as pass or fail.

On successful completion of the course i.e. after getting a pass grade in preparatory course, the candidates will be offered direct admission in July 2021 (Academic Year 2021–22) to the already allotted undergraduate course which was allotted to them during the time of JOSAA counseling 2020.

Filling-in of choices for preparatory courses is through the same online portal.

Candidates admitted to the preparatory course 2020–21 are also eligible to appear in JEE Advanced 2021 subject to fulfilling other eligibility criteria.

On successful completion of the course, the candidates will be offered direct admission to the already allotted undergraduate course.

Hope this will help