Mirror function not mirroring the way I want it to

Hi,

I'm trying to make a part out of a surface for a KVLCC2 Hull. I'm trying to mirror the hull on the Top plane to create full hull. When I go to do this on Insert>Mirror Component, it's mirroring in a weird way and doesn't just mirror onto the other side. Does someone know how to fix this? 

SolidworksGeneral