Here is the gradient as a reference.
Given this color reference, the result should be like the one in the screenshot. Select the shade layers and hit Ctrl+G to group them in a folder.
Proceed to create again a new layer above the shade folder. On this layer, paint a straight thin white line on the edges of the left and right wall. These lines will soften the edge of the wall.
Finally we will add ‘a life’ to the scene by placing a model at the edge point of the entrance. We will use this model for this purpose. Cut out the model from this image.
Add the cut out to the main document. Flip horizontally and scale down the size as needed. Set this model layer to normal at about 75% opacity.
Next we will add two more color adjustments for the entire scene. On the topmost position, create new adjustment layer (layer > new adjustment layers) and choose a selective color:
Another new adjustment layer: brightness/contrast.
Mask areas around the entrance, left wall, and floor as indicated in red highlight.
Create a new layer again (Shift+Ctrl+N) above the two adjustment layers. Take a very soft round brush at low opacity of about 10-15% opacity. Set this new layer to overlay blending at 100% opacity. On this new layer, paint soft white color to define casted light as pointed with an orange arrow.
To add the feel of sci-fi, we will add some light flares on the wall and floor. To do this we will paint the light flares. We do this on a separate document. Create another new document (Ctrl+N) with size given below:
Create a new layer filled with black on this new document. Take the brush tool (B) and hit F5 to show the brush preset. Set the brush tip and size as given. With light cyan color #53f6f8, click the brush once.
With a smaller brush, paint white color in the middle of the cyan color.
Proceed to set the brush tip and size as given below and paint a very light cyan color line (#c1fcfd) crossing the bright cyan round light.
Change again the size and tip of the brush and paint a bigger line with the same light cyan color.
Finally, change the tip and size of the brush again. With this setting, paint bright thinner white line. Select all the flare layers and hit Ctrl+E to merge them into a single layer. Name this layer flare.
Optionally, we can add layer style: outer glow (layer > layer style > outer glow)
Add the flare to the main document. Place the flare layer on the topmost position in the layer panel.
Set this flare layer to color dodge. Take a free transform tool (Ctrl+T). Squeeze the flare by hold-click and drag the middle left point to rightward.
Move the flare to areas where needed.
Duplicate the flare several times and add the duplicates to areas around the wall and floor. We can alter the color of the duplicates by giving prefer hue/saturation with a clipping mask.
Next create a new layer above all the other layers. Fill this layer (Shift+F5) with black. Set this layer to color dodge. On this layer, paint soft white combined with a bit blue and green color around the flares. This reference is given for inspiration.
Referring to the color given, the result should be like this: