As you have yet the "flat curve", seems there is no problem for have the C plane!

Let point any external point of the curve as Origine
click the Xaxe and move/point to the "oposite point" of the first external point
click the Zaxe and move/point to the "vertical" of the first external point
that's all ;)

Ps If you are losted look all views, and you can even use the "helpers' lines"!