Revealing mistake: When Carly's in her dream and attempts to use the elevator, if you look really closely, she doesn't actually hit the button that lights up.
Continuity mistake: When Carly and Sam are on the web show at the beginning, Sam puts the air hose around the edge of the watermelon. When the camera cuts back to the watermelon later on, the air hose is in the center of the watermelon.
ILike Jake - S1-E4
Continuity mistake: The locker that Sam has is introduced here, but in episode 3, she already has that locker.
Suggested correction: That's because the episodes were aired out of order, which isn't a mistake of the show. Episode 4, "ILike Jake", was the 2nd episode produced and episode 3, "IDream of Dance", was the 13th episode produced.
Continuity mistake: Sam pushes Freddie into the "haunted" apartment. In the very next shot, from inside the apartment, Freddie is standing up. In the next shot, outside the apartment, Sam is pushing the cart with Freddie's equipment on it and Freddie's voice says something like, "Ow! Quit it, Sam!" as if he is still lying on the floor. In the next shot, back inside the apartment, Freddie is standing up again.