There are a number of ways to adjust the point positions, both on the Monitor panel and by manually setting positions in the Applied Effects/Properties panel.
We can't give you specific instructions, however, without knowing which version of the program you're using and what your project settings are (as listed under the Edit menu). The method for adjusting effect's properties varies tremendously from version to version.
I am using PE 9. The project settings are AVCHD 720 square; 29.97 fps. Frame size 1280 x 720. The display format is 20fps Drop-Frame Timecode.
The image below is obviously from the monitor panel. The matte is diplayed - the circles indicate that it cannot be manipulated by grabbing the set points. I am concerned that maybe this option was not available in PE 9 - or do I access them some other way?
I have found that the visualization of the garbage matte bounding box points is not version specific.
The matter goes to having your Timeline video selected and the Garbage Matte Panel selected in Properties Panel (in your case)....however, the following is an example from Premiere Elements 9.0/9.0.1 on Windows 7 64 bit
Timeline Video Selected, but 16-Point Garbage Matte in Properties Palatte not...; consequently, no points seen to adjust.
Timeline Video Selected and 16-Point Garbage Matte Panel selected/highlighted in Properties Palette
Happens to me all the time, no matter what version. So, it has made a lasting impression.
Thank for the follow up. Glad that worked for you.
Continued success with your Premiere Elements workflows.