Continuity mistake: In the scene where Greg and Rowleys family are playing the game "I love you because..." the spinner they use keeps on changing positions in between shots.
Character mistake: When Greg reads the article about L'il Cutie being cancelled, cartoonist is misspelled cartoonish. The article also repeats the first column word for word in the third column.
Other mistake: When Heather Hills takes a swing at Rodrick with mike stand and hits the chocolate fountain, how does Heather splash chocolate on herself?
Character mistake: When Greg notices his yearbook picture, the pictures of each student are in alphabetical order by last name. On the row Greg is on, the order is mixed up; The order is: Holly Hills, Wes Hamby, Greg Heffley, Rowley Jefferson. The order should have been Wes Hamby, Greg Heffley, Holly Hills, Rowley Jefferson.
Plot hole: When Greg's father finds out that Greg lied about getting a job, one of the workers state that they don't employ minors. However they employed Holly as a tennis coach. She happens to be a "minor".