Matt,
The carbon ring should be at the end of the plug that is closest to the procelin. The part you can't see well, located behind the plug threads.
A 1-3mm ring would indicate your main jet was about correct.
You may want to find a nice magnifying flashlight to be able to even see the ring.
The other circuits need to be tuned by other methods than reading the plug.
Since the needle effects more than one circuit, it is one of the most important tuning items. The clip controls how far the taper of the needle sits in the carb, which can allow you to immediately change from rich to lean, or visa-versa. The taper profile of the needle also has an impact on the performance. Folks experiment with many different taper cuts.