The book I am searching for is a horror anthology; its short stories are written by various authors. It's aimed at young adults or older (I found it in my middle school library), and I believe it may have been published after the 70s but before the 2010s.
The first short story, I remember was divided in two parts. It was about a girl who goes to a party, where I think she meets a guy. Then she leaves, she ends up driving another girl who was also interested in the guy or something. While she was driving, the two girls are fighting, but then get in a car accident. The girl that was driving wakes up at the scene of the accident and realizes that the girl who was with her was dead. Since she didn't want to get in trouble, she switches places with the dead girl, so it would seem like the dead one was driving. Time passes, and the girl begins to receive weird voice mails from the dead girl and odd stuff is happening. At the end of the first part, the girl that survived realizes that she is the one that is dead, not the girl who supposedly died in the car accident.
Another story was about three best friends who are being haunted by their dead ex, who was dating all three of them at the same time. One of the girls dies when her radio (?) falls into the bathtub (at the same time, there was a greenish slime in the bathroom when the incident happened) after she hears the song that her ex and her liked when they were a couple. Her friends mourn her death, but when asking other people about hearing the song, they become surprised to learn that the couple song wasn't really playing on the radio when the girl died. The second girl falls down the stairs (the green slime was also there), and although she doesn't die, she won't be able to move anymore. I think she also heard the song that she liked when she was dating the guy before falling down the stairs. The third girl realizes that she is next when she is dedicated her couple song. She calls the radio station and after finding out no one requested the songs, she confesses that the three girls murdered their ex when they found out the guy was dating all three of them. The radio host calls the police, but by the time the cops get to her house, it's too late because the third girl was stabbed near the green slime.
The last story I remember well was one where a girl who was working at an ice cream parlor almost gets robbed by a guy she knows during her shift (?). To prevent him robbing her, she tells him the story of how she caused her teacher's death when she pushed a baby stroller on the road, leading to the car accident that killed her teacher. The guy then tells her that he wants her to show him the place of the crime scene, and she agrees to take him there soon. The guy leaves thinking that the girl was just bluffing. After her shift, the girl heads to her friend's house, and while they are watching a beauty pageant, the two girls agree to commit one last murder to make sure the guy doesn't say anything about the murder.
I would really love to find the title of the book because I really enjoyed the short stories.