Admit card is not much of concern but 10 marks sheet and 12 marks sheet are the documents that you required other than certificate like character and transfer certificate while getting admission in nit's and iit's. So, don't panic if you don't get the admit card.

Yes it is important to get admission,
You will be asked for the 10th board admit card during admission.
Why you are not getting your admit card,
Please mention the reason.