what does it mean roll back and save? idk how to get any endings
If you're playing on pc and use a mouse, you can use the wheel to scroll the text back which leads you to the previous screen and lets you save.
Though it's a demo so it doesn't have any endings at the moment. That message was left there since we planned to let people use old saves instead of replaying the common route but the full version won't be compatible with it anyway due to the new content.
So you can ignore the message and there are no actual endings.