Hello, hope you are doing well!

If you lost your admit card you can again download it from the official website in the same process you downloaded it earlier. Its not an issue if you have lost your admit card before getting it signed by the invigilator at the exam centre. So you can just check your email and download another admit card, or it'll be available if you log in to your Neet account at http://cbseneet.nic.in (http://cbseneet.nic.in/)