Continuity mistake: When Nancy goes to the police station in her dream, she looks down at Rod through a window as he sleeps in his cell. The first shot shows him sleeping completely on top of the covers but when Freddy enters the cell, Rod is partially covered with a sheet.
Continuity mistake: When Glen sneaks into Nancy's room, she has him turn off the lights and it is pretty dark in her room. When she wakes up to her alarm, it is still night outside but now it is a lot brighter in the room.
Continuity mistake: When Nancy is walking to school, Tina's boyfriend grabs her and he is not wearing a T-Shirt, only his black leather jacket. When she visits him in jail he is wearing a white T-shirt and the leather jacket. When you get arrested they don't let you have a jacket.
Continuity mistake: When Nancy leaves the kitchen to go to school, her orange backpack is empty, but when she storms away from her dad after he arrested Ron, her backpack is full.
Continuity mistake: Before Freddy kills Tina and takes her above her bed, the amount of blood on the sheets changes between shots.
Answer: The scene you are referring to is a dream sequence. In dreams everything is different and how they change throughout the movie is no mistake.
SAZOO1975