On her sixteenth-birthday, Junie’s best friend Joe warns her of her gangster-leaning, hip-hop singing, driving habits, but Junie won’t listen. She ends up crashing her birthday car into a ditch, almost killing herself. [Joe was right. The accident was caused by Junie's poor taste in music.] On top of her accident, Junie is attacked by a cello-toting homeless guy named Hagi who leaves her a cryptic note. When Junie gets to school the next day, [She has a car wreck so horrendous she almost dies, yet she's back in school the next day? I'd expect at least a two-week hospital stay.] she narrowly avoids a hair-pulling, nail-scratching catfight with her school’s bully, Rebecca Umpteenth, [Umpteenth? Really?] because Viscount appears in the school office. [Was she about to engage in this "cat fight" in the school office?] [And who is Viscount?] Viscount is one of the 25 immortals, [You're assuming I know who you mean by the 25 immortals, which I do, having read the query, but I think the synopsis should work independently.] and he tells her that she is in danger and she must leave the school now and go with him. [A stranger telling a 16-year-old to leave school is like a stranger telling a 4-year-old to come with him and he'll give her candy. Irresistible.]
Junie finds out from Viscount that because of her accident and almost-death the other day, the men become aware of her presence. She is the reincarnation of a witch named Riveya, who poisoned 25 men with her love potion in order to gain control of Crown Realm. [Whoa. And she buys this? Does he offer any evidence that this isn't just a wild fantasy story he made up to get her to follow him?] Viscount tells her that some men want to kill Riveya, and since she is her reincarnation, she is in danger. When Viscount leaves to protect Junie’s parents, [From what?] Junie searches through his base and finds evidence that she cannot trust his words. [This is backwards. If someone tells you you're the incarnation of a witch, you don't look for evidence that he's lying; you demand evidence that he isn't lying.] She finds evidence Viscount stalked her far earlier than her past birthday.
Eventually, Junie decides she can no longer be normal and teams up with Viscount, transporting herself to Crown Realm [Transporting herself? What does that mean?] to discover how to end the curse. Junie has to lie to her best friend Joe, who knows something is wrong and calls her trying to find out. [Apparently Crown Realm has excellent cell phone service. I was thinking it was in another dimension or something. Where is it?] She also has to lie to Rebecca, who has become suspicious and more aggressive following her kidnapping from Tev. [Tev? What's Tev?] Plus, Junie has no idea what to tell her parents about her sudden behavior. [I thought Junie was in Crown Realm. Where are her parents?] The police tail her [The Crown Realm police?] because of her connection with Tev's actions in kidnapping Rebecca. [You said Rebecca was kidnapped from Tev. Now it sounds like she was kidnapped by Tev.] [Why was Rebecca kidnapped?]
Junie’s efforts to uncover the cure for the love potion are thwarted by another boyfriend, Aren, who has is the reigning King of Crown Realm. Aren does not want to be cured of the love potion, because he likes being immortal. Aren wants to use Junie to kill the other immortals- or rather, immobilize them by decapitation. [The king should have an army at his disposal, which would be more efficient at decapitating 25 guys than one 16-year-old girl would.]
Finally, Junie comes head-to-head with Tev, saving police officers from his destruction. She wins with no help from anyone else. Her victory is cut short when she finds out her best friend Joe has been transformed into an immortal boyfriend himself by a witch from Riveya’s plan. [A witch from Riveya's plan? What does that mean?]
The synopsis seems highly disorganized. This will convince the reader that the book has the same problem. If you're convinced this book is ready to be published, I recommend going through an agent or publisher that doesn't require a synopsis.
A better idea might be to set the book aside while you work on another project or two and then read it and decide if it's salvageable. If the synopsis is an accurate summary of Junie's story, the plot may need an overhaul.