Ask your academic adviser if there is a preferred protocol at your college. Helping you with this type of issue is your adviser's job. If your adviser isn't very helpful or is difficult to work with, you can contact the professor directly. Personally, I would ask the professor in-person during office hours, but email or a phone call should be fine too.
When I was in college my academic adviser knew many courses for which the prerequisites were unnecessary, and it seemed as though the prerequisites for those courses were only required if you were majoring in that field, not if you were taking those courses as electives.
I didn't take any of the prerequisites for any of my 200- and 300-level psychology/sociology courses, or for my 300- and 400-level philosophy courses, and I did fine in all of them. At no point did I feel as though I had missed out on critical background information that would have been provided by one of the prerequisite courses.
The only time that I really messed up was when I registered for an animal science class as a fun elective, without realizing I had signed up for the advanced section instead of the beginner section. The beginner section was just horseback riding, but the advanced section also involved learning more advanced riding techniques and training horses. I was the only person who couldn't even begin to process the phrase, "go catch a horse and meet me in the stable." When I realized my mistake the first day and informed the instructor, she was very kind and let me stay in the advanced section, and made certain I received a little extra help when I needed it in the beginning.