it is probably one of the last parameters hidden away that is out. Look at the images below.
On the DVD Burning screen, click on Encoder settings
On the Encoder settings screen settings, click on Advanced
Check the Summary on the General settings tab to make sure that it has everything you want. On mine, the Aspect ratio: Auto (4:3 display) was not what I wanted
Click on the Video settings tab. Change the Aspect ratio to 16:9 display.
Don't change any other parameters unless you really know what they do.