Check out the link below and scroll down to the the question:
How do I delete a test date record?
To delete your scores for a particular test date, you must submit a written request. Write to:
ACT Institutional Services
P.O. Box 168
Iowa City, IA 52243-0168
(N.B. ACT's policy requires that the score was obtained from a paid registration (that is, not state or district-mandated testing) and has not yet been sent to any colleges.)
Wow! Colleges won't see your scores if you bombed your ACT test. What a relief? Now you can take your test with no pressure. And unlike the SAT you can actually see your score and then delete them. SAT allows test-takers until 11:59pm on the Wednesday following the test to decide whether they want to cancel their scores, but you won't know what your scores are. With the ACT you can see and decide to keep or delete your scores.