To keep in mind for the future, jessicaann, and seeing as how you are a photography student, there are urban safari classes available for photography students which include visits to abandoned buildings (mostly in the Detroit area), conducted by professional photographers who have had permission granted in advance by the police. The old Detroit railway station is one of the spots visited (and is a site also visited with some frequency by film crews). Wedding photographers often use these sites for wedding shots, as well, with impressive results.
The reason there is concern and special vigilance given the police over abandoned buildings, however, like the school whose property you trespassed on in Highland Park, is that these are areas often visited by those living on the edge of society (the druggies, the homeless, the mentally ill) and these are also areas where rapes and murders have occurred in the past.
Not too many years ago, a photographer-friend of mine was giving a tour to his photography students of abandoned buildings in Detroit and they stumbled (literally) over a decayed body. Trespassers have also been injured in buildings on rotted stairs and floors.
In other words, there is good reason not to trespass.
I agree with single317dad that having an attorney at least review your ticket and the facts would be smart. You do not want a misdemeanor on your record if there is any chance at all of avoiding one - and from what you describe, there is that chance to avoid one.
Good luck.
(as a note: what is described meets the definition of a "common trespass" violation in Michigan. See Highland Park Code Ordinance, Part 6, 668.06(b), Vacant Buildings - "No person, except an officer, employee or contractual agent of a governmental agency in the performance of a public duty, shall enter a vacant building or the property it is on without the express written authorization of the property owner, lessee, agent or trustee thereof")
