Your 9-patch image needs to be smaller than your smallest message. The system will expand 9-patch images, but will never shrink them in the 9-patch way. Also, make sure the name of your image file ends in ".9.png".
Here's an edited image that you can use in the Android Asset Tool to create your set of 9-patch images:
The following image shows how you should define your stretch regions in the 9-patch generator. You'll get a zip file with p-patch images in a few different densities. Put these into your drawables folders.