Translation:I don't have class tomorrow afternoon.
"I have no class tomorrow afternoon" would be correct. Reported on Nov. 19, 2017.
Am I the only one who doesn't like the 'class' there? it should be either 'any class(es)' or 'classes', but the 'class' on its own sounds bad.
You should also accept the future form for this sentence - and also the Position of the time indication can be at the beginning!
Although (school) class can be countable or uncountable, in this context it is better to see it as countable to avoid confusion with the other meanings of class that are exclusively uncountable. This is why "I don't have class" reads so strangely to many. No big deal but why can't we report what we feel are ungrammatical sentences to Duolingo, instead of always posting them in discussion threads?
Perhaps it's my upbringing, but 'class' to me means the group of people you study with, 'lesson' is what you do with that group of people.