As a student at WBCHSE board, I haven't got my HS admit card till now. What should I write in the roll no. section now?

You should get in touch with your school authorities and inform them that you have not received your admit card, as you might not be able to appear for the exam without your admit card. Get a card issued at the earliest. If your school authorities are unable to help you out, write to the WBCHSE boar