If you have the email with reg number, just take it with you along with proper ID to the test center. If you are nervous type, you can call ahead to the test center to make sure you are on the schedule.
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993