^ I guess it only matters if your school asks for a certain number of community service hours in order for you to graduate. Otherwise, just put it on the app as an internship.
After knowing that colleges don't actually ask for a "number of hours" on the application, I've stopped tracking how many hours I worked at a science museum. I think it's pointless anyhow, and unless you make it to the thousands of hours, 300 hrs is not going to look significantly more impressive than 100 hrs. It won't break or make your application either way.