With 5 beginner classes, you likely have separate sections for all of your beginner instruments. If you cut that down, you're going to have to have a doubled up class, such as double reeds/saxes, percussion/trumpets, or the like. (And it won't be things that make sense, it'll be what fits in the master schedule the easiest)
Yes, it's exhausting - but remember you also get paid more than core class teachers with your stipend, and that you don't have to teach a tested subject.
I would LOVE to have classes on the master schedule that weren't just "beginner woodwind" "beginner brass" and "beginner percussion" for my kids.