Example of a topic sentence in the beginning of a paragraph?

My First Day
My first day of college was a disaster. First, I went to the wrong classroom
for math. I was sitting in the class, surrounded by people taking notes and paying
attention to how to do equations, which would have been okay if I was supposed to be in
an algebra class. In reality, I was supposed to be in geometry, and when I discovered my
error, I had already missed the first twenty minutes of a one-hour class. When I got to
the correct class, all twenty-five students turned and looked at me as the teacher said,
"You're late." That would have been bad enough, but in my next class my history teacher
spoke so fast I could not follow most of what he said. The only thing I did hear was that
we were having a quiz tomorrow over today's lecture. My day seemed to be going better
during botany class, that is, until we visited the lab. I had a sneezing fit because of one
of the plants in the lab and had to leave the room. When I finally finished my classes for
the day, I discovered I had locked my keys in the car and had to wait for my brother to
bring another set. My first day of school was so bad that I know the rest will have to be
better.