Revealing mistake: Towards the end of the movie, the principal puts on his hat which turns his hair green. But you can see the green paint has already been applied before he puts his hat on.
Other mistake: Principal Dwight and Vice principal Stricker are fanatics of the rules and try to enforce them at all times with no mercy. However, when we can peek at the rulebook in Rafe's transcript, rule 52 says "only white, grey, khaki and navy", which if true would outlaw practically half of the kids we see at school wearing pink or yellow (yet they don't get scolded). (00:32:05)
Plot hole: Rafe is not a supernatural being, and besides not suffering any fatigue at all missing his sleep to do his pranks, some are outright impossible to execute and perform overnight for a person of his age (most likely for an adult in their prime too). Covering the entire hall and corridors, plus the principal's office, with post-it stickers requires a ridiculous amount of stickers to begin with, and arranging them creatively covering the whole walls, floor to ceiling, so that they create drawings, is an insane concept. Even more insane when it's the opening prank, anything he does later in the movie including the big movie finale requires less labor and time than his first act did.
Continuity mistake: Towards the end of the principal's lecture on rule number 1, down the street next to the bus you can see a boy with a flashy orange raincoat in the distance. Then he's on top of the school steps as the angle changes, mid-sentence when Dwight goes "You need to respect me." (00:07:50)
Continuity mistake: Rafe has just met the bumbling fool that is his principal: as Leo sneaks out of the building to meet them, behind Rafe a girl wearing white and pink is walking past them and getting into school. Several seconds later as the principal has already begun lecturing Rafe, the camera is back on him and the same girl is again walking behind him and getting to school. (00:07:30)
Continuity mistake: When Georgia brings the car to the front door on the first day, multiple continuity issues can be found (the car seems to go much further than it should, her hands get on and off the wheel), the most notable one being her braid that keeps switching between being in front or behind the right shoulder. (00:04:40)
Continuity mistake: When Rafe goes downstairs the first day, he's not wearing the backpack's strap on his left shoulder in the very first shot. But in the second, he has both, and shrugs it off. (00:04:15)
Continuity mistake: As the principal interrupts Jeanne, she has one hand barely touching the microphone shaft, turning into both hands clasped on the top in the following shot. (00:13:40)
Continuity mistake: In the car the first day, when Georgia says "Snitches get stitches" her arm goes from the top of the seat to the car window. (00:06:25)
Other mistake: When Rafe arrives at the new school, principal Dwight has his arms full of items he confiscated when the morning has not even started yet, very specific and obvious rule-breakers like a skate, 2 footballs and a basketball. So did some dudes just start playing ball and shooting hoops in front of the principal at 8 am in the middle of the street? Who are those rebels? There's no trace of rule defiance early in the movie. (00:06:30)
Answer: That's correct.