"Let Me Out" is an instrumental song that plays in "Mirror Gem" after Garnet tries to take the mirror away from Steven. Steven panics, slaps Garnet, and runs off apologizing. Garnet then tells the other Crystal Gems to "fan out" in order to find him. Steven panics, and asks the mirror what to do. The track ends as he successfully frees Lapis Lazuli from the mirror.
It also played again in the episode "Can't Go Back" after Steven wakes up from another Diamond-related dream and before Lapis takes off from the moon.