Yes, the JEE Main correction window usually opens after the registration process closes. During that time, you can edit details like registration number, name, category, etc. If you entered your 10th registration number instead of 12th, don’t panic, it’s not very serious and can be corrected when the portal opens. What to do: Wait for the correction window (generally a few days after form closing). Log in and update your correct 12th registration number. If it doesn’t allow change, you can email to NTA, with proof (12th marksheet/registration card). You’ll still get your admit card and can appear for the exam if other details are correct.