Nick and Norah's Infinite Playlist

A straight bass player in an "all gay band" called The Jerk-Offs, Nick O'Leary (Michael Cera) is a teenager from Hoboken, New Jersey. Nick is still heartbroken after his girlfriend, Tris (Alexis Dziena), broke up with him three weeks, two days, and 23 hours ago, and continues to make "breakup" mix CDs for her. Thom (Aaron Yoo) and Dev (Rafi Gavron), his gay bandmates who both hate Tris, convince Nick to perform at a club because his favorite bandâ the legendary, publicity-shy indie band Where's Fluffy? âis performing somewhere in New York City that night. Norah Silverberg (Kat Dennings) attends the same high school as Tris, Convent of the Sacred Heart, and though Norah and Tris dislike each other, they have a mutual friend named Caroline (Ari Graynor). Norah has not met Nick, but shares his taste in music based on recovering his mix CDs after Tris discards them in the trash. That night, the three girls end up at Arlene's Grocery on Manhattan's Lower East Side, where The Jerk-Offs are playing. Norah asks Nick to pretend to be her boyfriend to show up Tris. Norah kisses him, unaware that he is the ex-boyfriend of Tris. Caroline gets drunk and Norah wants to take her home, but Nick's bandmates (who see Norah as a potential new girlfriend for him) offer to take Caroline home so Norah and Nick can spend time together trying to find the show.
When Thom and Dev stop at Gray's Papaya for hot dogs, a confused Caroline escapes from Thom's van. Nick and Norah meet up with Thom and Dev to try to find her. A confusing phone call leads them to look for her at a club that "Where's Fluffy?" is rumored to be playing, but with no success. Tris, eager to win back Nick, catches up with them when she gets a phone call from Caroline, who is now able to tell Norah that she has "found Jesus" and "an altar boy without pants." They find a drunk Caroline on stage at a gay cabaret dressed as a Christmas tree. When they arrive at Nick's car, Tris is sitting on the hood waiting for him. Norah tells him how nice it was to meet him, but he leaves to talk with Tris without giving Norah a response. An upset Norah meets up at a club with her friend with benefits, Tal (Jay Baruchel), but soon realizes that he has an ulterior motive and hopes to get a deal for his band with Norah's father, a record producer (Richard Waddingham). She agrees to pay for Tal and his friends' drinks, but she tells the waitress to increase the tab because there was a miscalculation, and she leaves him to pay. Nick, meanwhile, decides to confront Tris, but she tells him she wants to be together again and asks for a ride home. Tris asks Nick to stop by the river, where she tries to seduce him. Whilst she seductively dances in front of the car, Nick reminisces fondly about Norah and the night's events and drives away, leaving Tris behind.
Nick calls Norah, apologizing for leaving, and she agrees to meet him again. Deciding to go somewhere where no one they know will find them, they arrive at Electric Lady Studios, a music studio owned by Norah's father. Once there, Norah gets Nick to play something he wrote in the studio, but then joins him in the recording room. Norah gets a text message from Caroline telling her where she found Where's Fluffy? playing. When they arrive at the show, they meet Tris, who cannot understand why Nick will not take her back, and Tal, who wants the same answer from Norah. Tal starts a fight with Nick, but Thom and Dev's friend, Lethario (Jonathan B. Wright), steps in and headbutts Tal. Nick and Norah share a smile and leave together. At Pennsylvania Station, Nick admits that he does not care about missing the concert, and they kiss on the escalator as the sun rises over New York City.

Question: Why does Nick call Norah?
Answer: to apologize