Same thing happened to me. Marked as blank for an answer, but when I looked at the scantron I got the right answer. Who do I contact? And is it guaranteed they will change my score? That one question would bump my score up +1 point
Eliminate as many answer choices as you can and then guess between remaining ones. But make sure to leave those questions that you do not get to read them in full due to running out of time blank so you do not inflate your score.