Other mistake: During Pacey's phone call to Joey at the end of the episode, Pacey lies about being on a fishing trip and mentions having caught a "91 pound marlin" which is a pretty big fish. This doesn't make sense for him to say that, as a fish that large would be noticably missing when he and Doug returned home. And they wouldn't have likely thrown a fish that large back into the sea. It would reveal he was lying if he returned home without the fish.
Other mistake: In the scene where Pacey and his Boss are out to lunch, his boss states that he just bought a car, so they head to a dealership. When they are walking in, his boss goes to a car that's kept in the showroom and dusts it off with a cloth as though that's the one he bought, since it is unlikely that he'd clean off a car that wasn't his. A car that someone just bought would not be kept in a showroom; it would be on the lot and ready to go, especially if the paperwork was already completed, as the boss stated when he said it was already signed and paid for.
Other mistake: After Dawson and Jen order "cokes" from Joey at the seaside restaurant, Joey pours their drinks into plastic red cups. She only pours several milliliters of cola into the cups, barely enough for one gulp. (00:29:50)