There's no bad ends so far. The difference is a TF on the plant altar and 4 conversations with the demon altar.
Also, I dont recomend building the gym yet unless you are a Patreon.
Do you get locked into the Demon Goddess Altar just by asking Q, or do you still get a choice later? (This doll did avoid getting her involved after realizing just what kind of shrine she'd be building, but it's still curious)
EDIT: Also, got the Gym trigger scene before whatever scene was supposed to precede it, by the looks of it.
EDIT: Also a box to click with something about updating to a May 2020 version? Weird.