Hello Aspirant

No, your school cannot deny your admit card for skipping your pre-boards.

Pre-boards are primarily practice exams to prepare you for the main board exams, they have nothing to do with your Admit Card that the Board of Examination publishes. The board actually has no clue about your pre-board exams and marks neither do they want to know about it because it plays no role in determining your marks in 12th.

While they are important for your preparation, they do not directly affect your eligibility to appear for the board exams. If your school still tells you so, show them the guidelines published by your Board of examination.