How do you open Castin’ Craft resin cans?
Prying with a narrow screwdriver is a good start. It appears in the photo that you have a bit of a start at the near edge of the top.

This particular seal is a throw-away and you can indeed stab it. Something stronger than a pointed stick should do well enough. A small blade philips screwdriver tapped in then bent outward will distort the top sufficiently to pop it free.

Be not afraid, plunge onward!