Preparing the mold.

 After the mold had cured i used a jigsaw to saw of the excess fiberglass and resin.

 Feels like this actually might work.

 After some bending and prying i managed o lift the plug from the mold. The release agent worked well. Last time I made a mold like this that did not go so well.

This is the almost finished mould. To do now is some sanding and building a frame attached to the mold. The frame will make the mold more rigid which is necessary when working with concrete. The finished stars will be heavy, about, 75 kg and it will probably take some force to get the finished casts out of the mold so it must be strong.