The book isn't over, but school is, and everyone rides off into the sunset.
Well, they run off into the sunset. Patrick, Sam, and Charlie, filled with the thrill of the last day of school (for Sam and Patrick, anyway), run up a hill into the sunset. "And everything was as good as it could be" (4.9.2).
Later, they go to Rocky Horror, and Patrick plays Frank 'N Furter one last time.
Charlie's sister even goes to the show, and she and her boyfriend dance the Time Warp.
The loser of the dance contest has to pretend to have sex with a stuffed Gumby doll on stage. Charlie doesn't want his sister to lose, so he gives her some tips before the dance. It's just a jump to the left, you know. And a step to the right…
Finally, they go to a party at Craig's house, and Charlie plays deejay: "It was a great way to sit alone at a party, and still feel a part of things" (4.9.9). That's our wallflower for you.