Hi Mark, so one center comes from the circle part here:



And the other one comes from the center of the 4 outer line segments here:



And having 2 slightly separated points for those means that the circle is not actually fully centered inside that rectangle, it seems like it is something like 0.02 inches above or below it.

Probably the easiest way to be sure you're getting just the circle center would be to select the main solid like this:



And then use Edit > Hide to hide it, leaving just your original circle curve being visible like this:



With the main solid hidden, it won't be targeted for snapping so you'll only have one snap point for the circle to target this way.

- Michael