Continuity mistake: At the restaurant, the chairs at the counter behind Mara and Tess get turned sideways a few times even though no-one is moving them. (00:08:36 - 00:09:19)
Continuity mistake: Before Mara goes into the bathroom to throw up, her hair is curled. After she throws up, her hair is almost straight. Mara's hair is curly again after she throws up a second time. (00:12:50 - 00:13:52)
Continuity mistake: The backgrounds visible while Joe is driving to get the drugs for Mara are inconsistent. There is or isn't rain on the windows and the foliage ranges from dense and green to sparse and orange/rust (Fall-like) coloring. (00:31:33 - 00:31:55)
Continuity mistake: When Joe Dalton is driving Jenna and Mara to pick up the drugs, a few yellowish-white flowers are dangling in front of him, but seem too far to the left (toward the driver) to be hanging from the rearview mirror. However, views from the back of the car to the front do not show any flowers. After Joe "explodes" and Jenna is trying to get into the driver's seat, there is something hanging from the rearview mirror (possibly a pine tree-shaped air freshener) that was not previously there. (00:31:39 - 00:32:25)
Continuity mistake: Mara is wearing a white long sleeve jersey when in the Dalton twins' car accident and when Dylan finds her in the water washing off blood. Dylan offers her the gray sweat suit he has in his backpack, but Mara says she isn't wearing it (because they wore those clothes at the police station). When Mara stands up, she has on a dark green T-shirt with a lighter green large circular design on the front. Mara is wearing the green top when she gets to quarantine, as well as later in the movie. This is obviously Mara's top, so where did it come from after she refused to wear the gray sweat suit from Dylan's backpack? (00:33:42 - 00:35:02)
Suggested correction: After rewatching the movie, I noticed that Dylan was POSSIBLY wearing this T-shirt under his jean jacket on his first day of school; the shirts look similar, but little can be seen because it is under the jean jacket. At the same time, Dylan's backpack at the accident scene did not look full enough to contain both parts of the sweatsuit, so it is a stretch to believe the T-shirt was also inside. Moreover, Dylan told Mara that he had a crush on her for two years, so the "old" T-shirt would have just happened to be in this backpack under the sweatsuit worn at the police station. Dylan is thinner than Mara, so it is unlikely that his T-shirt would fit her. When I rewatched the movie, I noticed that the T-shirt in question looked navy blue when Dylan had it on but green when Mara was wearing it.
Continuity mistake: The amount of Mara's cocktail [called "All of My Friends and Boyfriend Are Dead"] in the martini glass changes. She initially adds grenadine to almost the rim, but when she raises the glass, it is not as full. There also appears to be somewhat more in the glass when she sets it on the table for her dad. (01:07:50)
Continuity mistake: Mara's hair is inconsistent during the prom - the length and tightness of curls varies a few times. Most noticeably, the sides of her hair sometimes only reach her shoulders but other times look three or four inches longer (and this is not merely due to loosening of her curls). (01:14:20 - 01:16:06)
Continuity mistake: At the prom, Mara "spikes" the punch with a clear alcohol (tequila or vodka?) and the punch looks clear or a little cloudy/white. The punch is a pinkish color when Mara takes the bowl away and sits down. (01:19:45)
Continuity mistake: After Dylan explodes, we see Mara with a white bandage on her forehead. The bandage switches from left to right and then back to the left (and possibly changes size, but I am not too sure about that).