Why did she say "Wahlberg" not "(get, set,) go"?
This is an example of the speaker's sense of humor. Normally, the countdown used is "on your mark, get set, go!" However, when Gina countdowns, she ends with the last names of famous Marks in reference to the "mark" used in countdowns. Hence, “on your mark, get set, Wahlberg!" Mark Wahlberg is a famous American actor and the "Mark" mentioned in Gina's countdown.