"Mañana" = "Tomorrow"
"La mañana" = "The morning"
Exactly, you used were instead of are where the statement is about the current situation this morning. In terms of how you tell whether its a statement about something current or in the past (or even in the future, or generally over time as a whole etc etc), it has alot to do with the 'conjugations' used. In this case Tenemos means we have (not we had). Sorry but one of the (big) limitations with Duolingo is there's no easy way to search for the tips that have been helpful in the past so I can't point you to the relevant info about it in Duo. I did find this page online though https://www.dummies.com/languages/spanish/conjugating-the-irregular-spanish-verb-tener-to-have/ hope that helps!