Other mistake: When Gerald and Sean go to have lunch Sean asks his friend to bring them 2 sandwiches, and yet doesn't specify what type of sandwiches, nor does his friend ask Gerald what type he would like. He probably knows what type of sandwich Sean likes but he's meeting Gerald for the first time, so obviously he would have no idea what type of sandwich Gerald would want.
Other mistake: When Will is in his room reviewing books and flipping pages, the book "Help Yourself" is completely blank. (00:27:00 - 00:28:00)
Other mistake: When Will and Skylar are making out in her dorm room, Skylar says she won't sleep with Will again until she meets his friends and brothers. Then in the next scene when Skylar meets his friends at the bar, as they are walking out, Chuck and Skylar exchange "nice to meet you" comments. The problem with both of those scenes is Skylar has already met all of them in the Harvard bar where she and Will first meet near the beginning of the movie. In fact, she had a conversation with Chuck there.