Just had this happen to me as well. I'm going to use the bb.enablefreebuild cheat which unlocks build mode for you to add some helpful eco items to the lot. (I figured this out with the university pack. You can't use build mode in the dorms unless you use this cheat.)
I added two large wind turbines and some solar panels for the roof. Going to add some planter boxes as well for some magic seeds etc. Also just added some cool cc now to the interior! Will let you know how that works.
EDIT: I placed the wind turbines, solar panels, and some planters to help boost the footprint. There should be enough plants and trees on the lot but I added just a couple more. You have to stay and hangout on the lot for the footprint to get to neutral otherwise it will reset when you leave. Once I got it back to neutral I saved the game and it was fine when I returned. Again if you want it to be green you will have to hangout on the lot until it reaches the eco footprint you want. Hope this helps!
This happened to me also. I made the edits you suggested and it worked. On my way to a green lot!
