"We have a lot of activities tomorrow."
I'm wondering the same thing, it said 明天我们有很多活动 was wrong but then I dont know what the difference in meaning is
I think this is one of the cases of DL just not adding all of the correct translations. From DL and other sources I understood that there is no major difference between those two ways pf phrasing it.
My understanding of this is that that character is used before a future verb (e.g. we will run tomorrow, we will go tomorrow). The sentence here simply states that you have many things to do tomorrow, but is not talking about the act of doing them in the future. Does that make sense?