That's funny; when I gave it to another person to read she didn't like the wind line at all. I have kept it in, though, since I like it as well

I agree that the sentence with the homework was an incorrect modifier. It has been changed to:
Fortunately, the answers to half of the problems were in the back of the textbook (
why do teachers even bother assigning odd-numbered problems?), and through the use of techniques with dubious mathematical validity the homework was completed and stuffed into the backpack.
It's still a bit wordy and comma-heavy, but at least the correct person is doing the action now

is he sort of smushing and rolling his face around on it, deliberately making an big ol' smudge, or is he merely looking in, perhaps cupping his face to the glass because it's one of those windows that looks like a mirror from the outside, and his forehead and/or tip of his nose leave a smudge?
I was picturing the office building that I work in over the summer, and I forgot that not everyone would have the same image in their minds. What I thought was he just pushes his face to the (mirrored) glass in order to see in, and his nose and forehead leave a mark. I was in sort of an odd mood when I wrote this whole story, so I thought that was really funny. I'll look at the phrasing and see if I can make it a bit clearer what happens.
Thanks for the positive comments, everyone. When I have a final draft I'll post it again in case you really want to read the same story twice.