Thanks for your feedback! When you become the white ghost, you are supposed to run backward, all the way to the entrance. (you cannot shoot when you become the ghost.)
We should have made it clearer. As for now, after falling down to the cave, the only thing you can do is to go up, then immediately you will see a new path. so that’s it.
As for the key mapping issues, K might not be the best key to map as also pointed out by others. Nevertheless, we hope you can give it another try and, hopefully, enjoy it. Again, thank you for your feedback!