How to make Male and Female mould from curved petal surface

Hi please can someone help me in making a mould for my petal surface (attached). I need a male and female mould to put on a CNC router with a thin metal sheet between them to be press moulded. NOTE: there are no flat sides on this part.

I have tried to create a cavity mould but the option is grayed out for me.

I would really appreciate it.

SolidworksPlastics And Mold Design