If you plan to take it in the future, you're going to have to shell out another $400+. If not, then just don't show up.
This is from the
DAT examinee guide:
"No Show Policy - If you do not appear for your scheduled testing appointment and you do not cancel or reschedule your appointment in advance of the test date, you will forfeit all testing fees. You will be required to submit a new application and pay the fee to schedule a new appointment."