It's impossible to have cutters or moulds in all sizes. Let me show you a simple way of making a starfish freehand.

This is a part of the Seahorse Tutorial, that is why the size of the starfish is defined and the templates start from 31.

8.

Use a frilling stick (or a cocktail stick) to make dents as shown in the photo. Make a few larger holes in the middle.

You may need to rebend the arms.