How about something unexpected such as Katrina's admission that she has been secretly in love with her teacher as well? She is enamored by his intelligence and sensitivity, and that big muscles and a thick head such as the ones Brom Bones possess has never been to her liking. You could portray her something like Belle in Beauty and the Beast. A girl who loves to read and study and who values things in life that other girls her age don't...give her wisdom beyond her years and none of that superficial stuff. Katrina is no Brainless Barbie doll who is seeking a Ken Doll relationship.
As a result, Brom Bones attempts to scare Icabod away from Katrina by posing as the dreadful Headless Horseman, but Icabod, in a moment of intellectual inspiration exposes Brom for the fake he is, and Brom is the one found the next morning in a pumpkin patch with his "head" in his arms and a note for the town warning them to be careful of the stories they hear and pass along.
This sounds like a fun assignment, and one you should enjoy retelling. Let your imagination run wild, and try recording it into a tape recorder first. Then, simply play it back and right it down for editing and polishing.
Well, if I were you, I would try to be clever and amuse your teacher. You could definitely go for a comical "Scooby Doo" ending! Let's say that in the confrontation with the horseman before he can thow his head, Crane somehow manages to pin the creep to the ground. He rips off the cape, revealing that underneath its dark, voluminous folds is...
You guessed it... is Mr. Van Tassell! The father of the Katria Van Tassell, Crane's singing student, the one he wanted to marry! Well, her father would have none of that (you'll have to fudge a bit here...say Katrina had secretly fallen in love with him.) Desperate to stop the marriage at all costs, Van Tassell came up with this scheme to scare Crane away.
Why, if it wasn't for you meddling kids!! :)