Continuity mistake: When Jenna's boss puts the Sparkle magazine cover on the wall next to the Poise cover, they are only about 1/4" apart. This is very clear when he is talking about the numbers (11 vs 10) because they show a close-up shot of the covers. He asks a rhetorical question and Jenna raises her hand; from that point forward, the magazine covers are at least 1 1/2" to 2" apart. (00:20:45)
Continuity mistake: When Jenna is walking with the umbrella down the hall of her apartment, in the first shot the umbrella is latched closed and Jenna unlatches it so that the umbrella can open up. In the very next shot it is back together, then it's unlatched again. (00:15:35)
Continuity mistake: When they are at the party for Poise, Matt is dancing along with the group. If you look closely at his legs when there's a close-up of Richard, he's already stopped dancing. The next shot, he stops dancing and tells Jenna that he has to go.
Character mistake: Jenna has Sparkle letters at her work. Wouldn't she get caught earlier?
Answer: Jenna asked the girl, "Can you tell I'm wearing underwear? Because I totally am". This is because when she was 13 just a day before, she was wearing big underwear. Now she's wearing a thong, which wouldn't be visible when wearing a dress.