There is many ways to do this.
One way is to make a top layer, that has 0%,0% parallax (like your UI layer).
On start of layout you can hide this layer by setting the layer to a opacity at 0%.
On collision with your player, set game time to 0, and then set your "game over' layer to opacity to 100%.
Add game over music and a add a space bar key to restart layout.
Remember to set game time to 1 again at start of layout.