An App Doesn't Fill The Screen
Most
apps for iPhone and iPod touch can be used with iPad, but they
might not take advantage of the large screen. In this case,
tap 
to zoom in on the app.
Tap 
to return
to the original size.
Check the App Store to see if there's a version of the app that's optimized for iPad, or a universal version that's optimized for iPhone, iPod touch, and iPad.