Hi Brian
If i understand correctly . Try decreasing the thickness of the part
If your part is setup as being 1/8" Decrease that to 1/16" and set cut through to zero
or leave it as is and set cut through at whatever depth you want . Say -025

 

Have you looked at the instructions? Click on the question mark icon.

Here is how to change the depth for the centerline tool.

Center line Tool - This tool is used to define a center line cut on a SketchUp edge. The common use of center lines, is to cut a shallow graphical design or slot. If you are able to draw the necessary pattern of lines to form a pocket, you can also use center lines to cut out the pocket. Pocket milling is when you cut out shallow openings, that doesn't penetrate to the other side.

It automatically selects all connected edges. Press the ["Shift" key], if you only want a single edge.

Use the ["Left Arrow"]["Right Arrow"] keys to scroll through the preset depths: [25%, 50%, 75% & 100%]. This will result in the cut depth, as a percentage of the material thickness. You can see the current depth factor in the VCB (lower right hand corner in SketchUp).
Use the ["Down" key] to set the depth back to the default of 50%.

Note: You can type custom depth values into the VCB, using your keyboard. The value is not accepted, until the "Enter" key is pressed. Then the % suffix will appear with the VCB value, which indicates the value is now set. Max value allowed is 140%.

 

Beejay, what you have missed is reading the SketchUcam help (big blue question mark on the right end of the toolbar) and watching all the instruction videos (linked from the 'How to install' message at the top of the Download thread on this forum). These resources will give you a head start on using the system to the fullest extent.