[@LokiLeo789], I'm with Termite here. A whole galaxy is in no sense 'very small'. As we've been using the demiplanes, there is no formal limit on their physical extent, but generally things get pretty featureless if you go too far away from the middle. The point of the size restriction is so you "don't think you can go creating a separate universe in your own plane." An entire galaxy contains enough stuff to be effectively a universe as far as people (or even gods) inside are concerned.