Hello Madhur! For this mistake you need to contact them through their emails and send them email regarding this problem and ask for help to change your roll number. You can also contact them on phone to get it corrected.

Here are their contacts: https://www.google.com/url?sa=t&source=web&rct=j&url=https://jeemain.nic.in/WebInfo/Public/View.aspx%3Fpage%3D80&ved=2ahUKEwjQhOvf-ZriAhVDT30KHRX1CHUQFjAAegQIARAB&usg=AOvVaw2_G2vJw5gdc_uCJsrahhwC

Hope this helps you!