Pinpointing where it went wrong.
I quite enjoyed parts of this, but in my opinion this is where I felt it struggled:
-The bookends were both far weaker than the middle: The second act was actually a very solid piece of pdycho-horror writing, but the opening didn't set it up correctly and the movie didn't pack the punch it should have.
- Use of characters:
The girlfriend was an underused mess throughout the film, and the side story of the girl and guy who actually did go to prom didn't go where it needed to. In my opinion that side story would have been effective if they were given multiple chances to discover what was happening in the main story but kept missing them, so we actually felt like they might contribute to the story at some point. And the cop dying was a great idea but not if every other character is also unimportant. It makes it far less surprising when you don't even expect him to matter.
That's what I boiled it down to essentially. Just a bit of narrative inexperience but there were definitely strong moments amongst it.