"You just left school"
Is 'just' subtly represented in 'umetoka' or should I report it as superflous?
"You left school" would be ulitoka shuleni. Umetoka shuleni is immediate past, which is why the "just" is in there.
If I were to report it, I'd do it more on grounds of grammar. "You have just left school". As it is written it sounds more like you just upped and left without saying anything, rather than talking about something you did a short time ago.