It’s difficult to predict actual rank or JEE advanced qualify marks. you may calculate your expected rank by this formula

100 - your total percentile score is the percentage of people ahead of you. 869010 are the number of candidates appeared for Jan exam. So rank formula is (100 - your total score) X 869010 /100. If the number of candidates for April exam increased to 1200000 then your final rank shall be (100 - your total score) X 1200000/100

So your rank might be around 20000. But it may change as more students register in April Exam .

So it is advisable that you study more to get more percentile so as to secure a good rank .

Yes , you will surely get CSE in various NITs like NIT Silchar , NIT Srinagar, NIT Uttarakhand , NIT Goa