As an alternative, you might use a 9 patch image as the background for your layout, allowing for more "natural" shadows:
Result:
Put the image in your /res/drawable
folder.
Make sure the file extension is .9.png
, not .png
By the way, this is a modified (reduced to the minimum square size) of an existing resource found in the API 19 sdk resources folder.
I left the red markers, since they don't seem to be harmful, as shown in the draw9patch tool.
[EDIT]
About 9 patches, in case you never had anything to do with them.
Simply add it as the background of your View.
The black-marked areas (left and top) will stretch (vertically, horizontally).
The black-marked areas (right, bottom) define the "content area" (where it's possible to add text or Views - you can call the unmarked regions "padding", if you like to).
Tutorial: http://radleymarx.com/blog/simple-guide-to-9-patch/