I am almost certain (99%, unless something changed up on me) that you cannot cancel your score. Unlike the MCAT which takes weeks to be graded, the DAT will give you your results right after your test. So the minute you sit down, everything counts, time runs up, you get your score. Best of luck.
oops. almost forgot to answer your first part. You get your scores right there after your test at the center. They print it out, stamp it and sign it.