Other mistake: Before the hall monitor folds the note into a paper airplane, the note has creases as is it was already folded into a paper airplane, and then flattened out for a different take.
Other mistake: While the school is burning, a few shots after the closeup of Kate and Tom kissing, there's another shot of an explosion and it's a flipped shot, note the writing is backwards on the banner. (01:30:10)
Other mistake: In the scene where The Ramones are playing "Pinhead", they say: "D-U-M-B" as the letters appear in a very big size. But when they say it again, it appears like this: "D-M-U-B." (01:08:30)