When Cameron and Amber kiss on the couch "Fade into You" by Mazzy Star is playing in the background, a song which didn't premier on MTV until late October 1993, whereas the movie takes place in the summer of '93.
When Brandy (Aubrey Plaza) sings The Wind Beneath My Wings, to get back her friends, Wendy (Sarah Steele) makes a reference to the famous Jerry Maguire "You had me at hello" line, which was only released in 1996.
The phrase "Shut the front door!" was not in popular usage in 1993. That phrase originated with radio personality Jason "Buckethead" Bailey on his show "The Buckethead Show" on WJRR in Orlando, Florida, which didn't begin airing until 2000.
When Brandy tells Fiona that Fiona missed the turn, Brandy points forward and continues to point forward. If Fiona had missed the turn, they would have already passed it, so Brandy should be pointing backwards.