Hello Rupa. Your Jee percentile score tells you the exact percentage of students ahead of you. That is 77.45% of tot. students appeared are ahead of you. Now tot. students appeared in January exam was approximately 8,74,469. Imagine 77.45% of 8,74,469 students ahead of you i.e. almost 6,77,276 students are ahead of you. 

So I would recommend you to study hard for April exam as NTA will consider your best of both attempts and then declare the overall merit list.

Also the college cutoffs cannot be determined now because it will depend on the no. of students appearing in the April exam and also on the best of two attempts by candidates appearing twice.

For now you can calculate your rank from below formula.

Rank - (100-percentile score)*(874469/100)

But this is oviously not your final rank as it will be different if the total no. of students appearing in the April exam changes (most oviously no. of students appearing in April will be higher).

But from the previous cutoff I can tell you that any rank below 2,00,000 will get you qualified to sit for JEE Advanced.

For more details you can check the below link.

Https://www.entrance360.com/engineering/how-to-calculate-rank-for-jee-mains-2019/

Hope this helps. For any query you can comment down below.