Contact them tommorrow, it would save you lots of trouble at the test site. I had a similar situation where my first and last name was switched, but it was not much a problem and they still let me take the test at the day of the test. The only thing they told me was that they need to file a report notifying my situation so that i can obtain my score when im done witht DAT. Just remember to bring your ID and a credit card or bank debit card!!
Hope it helps!
