The way I picture it - you're mixing Plantuml's single-line syntax (using \n) where everything should fit on one line, with Plantuml's multi-line syntax (using note/end note) where you use real carriage returns.
So Plantuml's answer is to continue with using note/end note but turn all the \n into real carriage returns using %newline().
I'll give the opposite answer: Keep the \n, but change the note into a single-line format note:
note right: $note_text
