If you've done your mask correctly, you will have arrived at something like this.
Step 13 - Add some Blue
Create a new Layer (Layer > New > Layer). Select the bottom of the document. A good way to do this is quickly and accurately is to select the "mountain copy" layer because you know that it is half of the screen. To do this, go into your layers palette, select the layer "mountain copy" (control/command + click on the icon for the layer "mountain copy").
Note: If you cannot seem to select the layer by clicking on it, you are probably clicking the wrong thing. To the left of the layer name, there is a small icon of the layer. You should control/command + click on that image, not the text itself.
Select a blue for your foreground (I choose #216a82) and black for your background, and create a gradient. Set the opacity for this layer to 50%.
Step 14 - Lens Flare
Create another new layer (Layer > New > Layer), and call it "lens flare". Fill this layer with black using the fill tool (G), and then head up to Filters > Render > Lens Flare. Select 105mm Prime, and leave the brightness at 100%. Then center the lens flare as best you can (if you miss the center you can always undo and try again, or just move it using the move (V) tool)0.
Using these settings you should get this:
Step 15 - Up the Contrast
Go to Image > Adjustments > Brightness/Contrast and move the contrast to the highest level possible.
Step 16 - Colorize
Go to Image > Adjustments > Hue/Saturation and move the mimic the settings below.
Step 17 - Checkpoint
Just look at your layers palette and make sure that your layers are like this (order and number of layers should be the same as this). Then, set the blending mode for the layer "lens flare" to linear dodge (add).
Step 18 - Another Lens Flare
Duplicate the Layer (control/command + J) and press (control/command + T). Shrink the height and expand the width of this flare to either side (try to copy the picture below).
Step 19 - Blur It
Go to Filter > Blur > Gaussian Blur, and apply a blur of about 7px.
Step 20 - Center It
Move the flattened and elongated lens flare up to the center line.
Step 21 - Center Gradient
Create a new layer (Layer > New > Layer), and select your gradient tool. Choose the reflected gradient option, and using a blue foreground (I used #216a82), create a foreground to transparent gradient from the center. To do this correctly, you will want to start in the center and click and drag to either the top or the bottom. When you're done, se this layer to 50% opacity.
Step 22 - Creating the Grid! -- A
Create a new layer (Layer > New > Layer), and set the background to black (this is so you can see what you're doing... DO NOT put anything on this layer in later steps besides the black color that is already there!). Press (U) and select the rounded rectangle tool. Set the radius to 50 px. Also make sure that you're on paths, not shapes.
Step 23 - Creating the Grid! -- B
Holding shift to ensure that your drawing perfect squares, create a rounded rectangle like the one below.
Step 24 - Creating the Grid! -- C
Create a new layer (Layer > New > Layer), name it "grid", and make white your foreground color. Right click in the box and select fill path.