Trying to mirror a feature with fillets

I am trying to mirror a feature with fillets from the left side of a mold cavity to the right side. This is the runner entry into the mold on the left to the right side.

It is asking for a reference plane but the feature does not accept the plane I have created.

Is there a easier way of doing this or am I missing a input needed?

Can somebody explain or help?

SolidworksParts And Features