What shall be my category rank in this general rank??

Again mains is there

How many percentage should taken for eligible

The category rank will depend upon the number of students appearing from that particular category. JEE Main Examination again will happen in April so the final rank will again depend upon the number of students appearing from that particular category. That's the reason the category rank cannot be predicted as of now. I suggest you to wait for the officials to announce the actual figure. 

Yes you can apply for JEE Mains again which is going to be conducted in April. There is no cutoff percentile to be eligible to give JEE Main again in April.