I think yes, "kulala mapema" would be also translated as "to go to sleep early".
Here some example sentences (I think these are more advanced because they are conditional sentences)
Ungeona televisheni ungelala mapema.
[If you were to watch television, you would go to sleep early.]
Usingeona televisheni usingelala mapema.
[If you were not to watch television, you would not go to sleep early.]
From KU (University of Kansas):
B). Negation with the Tenses [vikanushi vya nyakati] / vi.
I've heard it both ways tbh. It should be accepting both, if not just use the report feature during lessons, because the reports go directly to them, instead of them looking through the comments.