I'm worried that when I masturbate at night on my bed, the next day at school people will know I've been masturbating because of my smell. Also, if I don't smell, will my sheets or clothes?
Either way, I seriously doubt it. Think about it – have you ever thought someone smelled like they just masturbated? Or heard anyone say someone smells like they masturbated? Didn't think so!
Your "paranoia" suggests you aren't comfortable with the idea of masturbating, so you feel guilty about it. My advice would be to work on these hang-ups rather than worrying about it so much.