You will need to take with you your Confirmation email printout ot on mobile device. According to the official website https://www.nmat.org/nmat-by-gmac-exam-terms-and-conditions/, it says that you will need:

1. Confirmation email printout ot on mobile device.

2. Admit Card

3. Any other document as advised by GMGC for PWD Candidates

4. Valid Photo Id and another Signature Id.

Rule 16.5 says that Candidates who are unable to produce these documents will not be admitted into the testing room and also not be offered a test fee refund. So Confirmation mail is important. Please check your spam folder and if you haven't received it there as well, you have to reach out to them at: nmatbygmacsupport@merittrac.com (mailto:nmatbygmacsupport@merittrac.com)