There's an issue that you cant change position/exit the door whilst you're attacking and with auto attack on, you usually won't be able to leave until the mob is dead. i believe clicking on your character will fix that, as the game will attempt to run a heal action on yourself but will fail to do so unless you've got a heal selected. So after clicking/pressing your character you should have been able to leave.
much easier to disable this, especially for HC, but this will mean you will need to press/click for every attack.

I would also recommend SC until you figure out wtf is going on, makes no sense to make a HC char first when you don't understand what the game is doing.