Debian – How to get full screen resolution with Debian

I have an HP 20wm monitor that I use for programming, which has a resolution of 1600×900. But whenever I try setting the resolution to 1600×900 it gets cropped on either side to 1440×900, so when I adjust the monitor setting to full screen it just stretches the image, which looks wrong. cvt 1600 900 outputs the following:

# 1600x900 59.95 Hz (CVT 1.44M9) hsync: 55.99 kHz; pclk: 118.25 MHz
Modeline "1600x900_60.00"  118.25  1600 1696 1856 2112  900 903 908 934 -hsync +vsync

I set the resolution using xrandr as follows:

xrandr --newmode "FullScreen"  118.25  1600 1696 1856 2112  900 903 908 934 -hsync +vsync
xrandr --addmode VGA1 "FullScreen"

This is what I get on either side of the screen:

How do I fix this?

Even stranger, when I go to display under preferences it says 'Resolution 1600 x 900' when that is clearly not the case. xrandr reveals the following information:

Screen 0: minimum 320 x 200, current 1600 x 900, maximum 8192 x 8192
LVDS1 connected (normal left inverted right x axis y axis)
   1366x768      60.03 +
   1360x768      59.80    59.96  
   1024x768      60.00  
   800x600       60.32    56.25  
   640x480       59.94  
VGA1 connected primary 1600x900+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768      60.00  
   800x600       60.32    56.25  
   848x480       60.00  
   640x480       59.94  
   FullScreen    59.95* 
HDMI1 disconnected (normal left inverted right x axis y axis)
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)