Ok i see what you are asking i think

ABS plastic used in vehicle interiors is a funny beast and like epoxy and polyester resin it is heat/catalyst cured BUT you cant repair abs plastic with either as it wont bond properly but will take heat of over lay and not dis form but will bond enough to stay on the product . To take a mold off a item it involves multiple layer's of casting resin and fibreglass which will dis form normal plastic due to the thermo cure

you say a sheet is this flat ? if so use a pane of glass , or get your self a vacuum table a 1mm silicone sheet layed over the product you want to copy then cover resin in fibreglass then bag it to the vacuum table until cured

but 1, if you could find a plastic abs to spec it will expensive 2, above will be so much more easier