See predictions aren't absolute that's the reason why it is called prediction. I think you have used the career360 predictor tool. Now as you know every year the exams are conducted and every year there are variations. So in career360 they have experts who analyze the data and build the predictor. So based on the past trends and based on your shift hardness and analyzation, its predicted that you can get such percentile. As a result you may not get exactly that percentile but you will surely get in the arena of this percentile range.

For the JEE MAINS rank predictor visit the link provided below:

To know more about JEE MAINS college predictor visit the link below:

I hope this answer helps. All the very best for your future endeavors!