Goofs

Right before the shooting, Eric glances at his watch, which reads "WE", indicating that it's Wednesday. April 20, 1999 was a Tuesday.

In the film, Rachel attended prom with an Asian classmate named Kevin. In real life she went with Nick Baumgart.

In the film, Dylan drives Eric around. In real life, Eric had his own car.

There is no definite confirmation that Eric asked Rachel anything at before she died.

Rachel was having lunch with Richard Castaldo, not Dave Rogers.

Dylan and Eric play a single player video game with two controllers.

The convenience store has Monster Energy drinks, which first came to market in 2002.

Dubstep was not a musical genre teens would listen to in the 1999 because it did not exist.

The convenience store has Rip It energy drinks, which were introduced in 2004.

An establishing shot of the school shows a sign that reads "Frank DeAngelis Field"; the field wasn't called that until the early 2010s.

The scenery is too green and lush for Colorado in April.

The Tennessee Tower in Nashville can be seen in the background during the rooftop scenes; the movie is set in Colorado.

The Columbine Shooting occurred in Denver, Colorado, but seemingly little to no effort was made to make the film appear as if it were set in Denver. All of the rooftop scenes show a city far smaller than Denver, surrounded by flat woodlands or green rolling hills. Denver is surrounded by the very tall Rocky Mountains and has no woodland areas.