Yo. What if the galaxy size is dependent on the embryo? Can your cube be the size of my Universe?

The concept of "galaxy size" is not relevant to the development of a human embryo, as the embryo's growth occurs within the confines of the human body and is governed by biological processes rather than astronomical scales. The development of a human embryo involves complex cellular and molecular changes, but these occur on a microscopic level, far removed from the cosmic scales of galaxies.