A saved scene file is not the same thing as a node.
get_node() is used to reference a node that currently exists in the scene tree. For example, if you have a "Main" scene, and you instance your player scene in it, you can reference the player with
If you need to instance a scene that has been saved, that can be done using the UI by using the Instance button (its tooltip says "Instance a scene file as a Node"), or in code like so:
onready var player_scene = preload("res://Scenes/Player/Player.tscn")
var player = Player_scene.instance()
You didn't include what your scene setup is, so you'll have to adapt accordingly.