Hello aspirant, hope you are doing good.

So, first thing that you need to know is that the preparatory rank is not a real rank, and it doesn't give you a confirmed seat in any of the colleges this year. This rank is for preparatory courses, which are offered by some of the IITs for a year, and at the end of the year, you have to qualify for the exam, only then you will be able to get a confirm seat in the IITs. These ranks doesn't let you get into IIST, it's not for IIT preparatory courses.

If you want to know about all the possible colleges you can get into with your JEE Mains rank, you can get it here:

https://engineering.careers360.com/jee-advanced-college-predictor?icn=QnA&ici=qna_answer

Hope this helps you. Good Luckk!!