Catholic high school. Mid-to-late 70s. No pool, no swimming, but we did change out of our school uniforms into jockstraps and gym uniforms for PE, and we were required to shower after class -- no exceptions, no excuses -- in a large gang shower (yellow-tiled, I believe).
I don't recall any anxiety about this. What I do remember is a few of the more muscular bodies, and which guys had larger dicks (Kevin M!--who would have thought it?), and the name of the boy who (although he had terrible acne) had a truly outstanding butt. Ah, Gary, I hope your face eventually cleared up, because in every other way, you were fine.