The point of the bad ending was to show that Jenna isn't too different from the people she criticizes. What better way to show that than to have her do what Heather would have done? There's hints here and there to her selfishness and lack of self-awareness and her overall derisive attitude towards others. It's not surprising what happens when you provide her with enough excuses to head down that path. Micha and Leo are honest enough to call her out on her her bs while Chase is a bit of a simp so you won't that impression from his internal monologues...
so it's a good thing it's actually up to Sam to set her straight