Dear RIYA, don't be confused with this.
Yeah it's very much true that one can be rejected in the counselling.
See, the scenario in counselling is -
The college mentions a range of ranks and asks all the students who are in the range to attend the counselling.
During the counselling day, the college selectors
select the top most rankers first and according to the seat matrix they start calling the names.
For example-- An XYZ college has 100 seats. And it has metioned the range to 100-280 rankers. On the counselling day. The college will first select 100th rank student and then it will move on to other. The calling of Reserved candidates is done in the same way. They fight for the reserved seats. Like the same college above has 15 seats reserved for ST  candidates then all the ST students can only fight for those 15 seats.
As soon as all the seats filled up, rest all the students are asked to go.
Like XYZ college's 100 seats got filled up and still there are many students who didn't got the seat then they can't do anything.
So all the very best.
Don't worry if you have a good score then you will definitely get a seat.
And one more thing generally many students don't even come to attend counselling, so there seat is given to next lower rank student.
Hope this helps:)