The case is still looking flat on the top so were going to add shadow details. First go to Select > Load selection > Default to select the entire case then grab the Lasso tool and cut out 50% of the selection in the middle.
Create a new layer and fill selection with #00000.
Go to Filter > Blur > Motion blur > Angle: 90 || Distance 16 px.
Set the blending mode to Hard light and opacity level of 7 %.
Picture guide is cropped to show the important of this steps please see the final for a better look.