When his mother is being kissed by Jude on stage at the music festival, Jake is clapping instead of filming, yet a sequence including the kiss shows up in his movie.
During the full-moon dance/party, there is a long shot of the full moon through the trees followed 10 seconds later by an extreme close-up of the moon that is clearly not full.
In the film, the town of Woodstock, New York is portrayed as the geographical setting for the music festival bearing its name. In fact, the festival, while originally intended to be held in Woodstock, was ultimately held in Bethel, New York - over 50 miles from the town of Woodstock.