"David didn't mean to do anything wrong! He just found the old metal armband in a box of junk and thought it looked cool... He strapped it over his wrist, and all hell broke loose."
Here's where your hook starts:
David Judd never wanted to be friends with a bunch of ghosts and goblins, but ever since he accidentally opened a portal to another dimension, he's been the most unpopular kid at Prairie Middle School. His "Dark Planer" pals – led by the charismatic poltergeist, Jallywag – keep getting David into twisted, magical mischief. But when the cheery new girl, Jillian Nichols, offers David an unlikely friendship, he is inspired to change his fate. David ends up grounded, suspended from school, the target of international bounty hunters, and unintentionally flooding East Deerfield with hundreds of otherworldly party-crashers. Fortunately, David is used to a little adversity. Once David confronts his fears, the horde of Dark Planers, and the nightmarish vortex, East Deerfield is back to normal... or as normal as an inter-dimensional portal can be!
and here's where it ends
THE BOY WHO RUINED EVERYTHING is a 40,000-word, middle-grade novel about the awkward tween years, peer pressure, and family values in America's haunted heartland.
This is energetic writing but it's not saying much. He hangs out with a bad crowd till a woman shows him the error of his ways. That's a yawn in any dimension.
What's going to happen if he doesn't confront his fears? What's the conflict? Demons arriving in middle school is an event, not a plot.