Dear student,

Only your rank doesn't decides that whether you would get a particular branch or not. There are only few seats and the number is fixed, if you did not get your first choice then the possibility must be there that someone else might have got that particular seat. Someone else with a higher rank might have filled the same choice as you did, and as he/she had a higher rank, he/she got that particular seat. Whether a person gets a particular seat doesn't just depends on how high rank he/she gets, instead it depends on the fact that the person has a relatively higher rank than others.