Hey, there! You can change the size of the capture and the CRT on your second display. In the zip, there's a file called "SuperCRT.ini". You can modify the values for the capture window. Change it to the values below and you have a full capture for your average monitor.
SrcX=1920
SrcY=1080
The CRT display window can also be resized for viewing but clicking and dragging the bottom right corner to fill your screen. Enjoy!