Other mistake: A poster in the school states that the Academic Decathlon takes place on October 14-15. But later on in the movie, another poster says it's on September 14.
Suggested correction: Was in a similar thing in HS. Not too surprisingly, we had more than one event throughout the year. In fact, I've never heard of an extra-curricular with only 1 event. Likely 2 different meets.
They said later on, though, and that would go into the next school year, which is weird for most extracurriculars to have pre-planned events for the next school year.
Other mistake: When Loki gets up from being thrown during the "get help" scene, he seems too far to the left of the screen (Thor's right). Thor is still looking down to his left at the fallen guards, and in the previous shot we saw that Loki fell amongst them as he knocked them down.