Continuity mistake: When Nancy lays in bed, she looks up at the wall, just after it has been streched by Freddy. In the wideshot her left arm falls off the pillow, yet in the next closeup it's back on the pillow resting by her head. (00:13:40)
Continuity mistake: After the bathtub scene, when Nancy opens the mirrored medicine cabinet and removes the bottle of Sta-Awake, her fingernails are short as usual, but in the bottle's closeup Nancy's fingernails are quite long. (00:34:10)
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.
Continuity mistake: After Rod's funeral where Nancy's mother is about to get into her car, there's a shot of her saying "I'm going to get her some help". There's a gravestone behind her that reads "Coulter". When we see her entering the car, with her relative position unchanged, the gravestone reads "McRenolds" (00:47:05)
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