Volunteer or not, profit or not, what you're doing amounts to copyright infringement. It's NOT Fair Use, it's a wholesale copying of several other copyright protected works, and making of a derivative work without permission of the copyright holder. When you press "record", you begin making a duplicate (albeit low quality due to the
microphone) of the song being played through gym's loudspeakers. When you upload the video to YouTube, you're making ANOTHER copy, and when the video is streamed to users, there's an unauthorized performance of the copied work. YouTube's algorithm is rightly catching this, and taking your videos down. If they don't, they could be liable for Millions of dollars in damages. (the DMCA requires that they implement these kinds of procedures, or lose their so-called "safe harbor") So, they have to be vigilant. The school has a license to make a "public performance" of the song (this is what
ASCAP,
BMI, and
SESAC are all about... public performance licensing) But, the license does NOT authorize the recording or making of derivative works based on the song. That would require direct permission from TWO different owners. First, the owner of the musical composition (the music publisher representing the songwriter), and second, the record company that owns the recording being used. It may seem oppressive, even silly, but it's the legal framework under which these entities (the publisher, record company, songwriter and artist) get compensated for making the investment in writing, recording and marketing the music we enjoy and dance to.