“Space,” like “time,” is a relational concept. It does not designate an entity, but a relationship, which exists only within the universe. The universe is not in space any more than it is in time. To be “in a position” means to have a certain relationship to the boundary of some container. E.g., you are in New York: there is a point of the earth’s surface on which you stand — that’s your spatial position: your relation to this point. All it means to say “There is space between two objects” is that they occupy different positions. In this case, you are focusing on two relationships — the relationship of one entity to its container and of another to its container — simultaneously.
The universe, therefore, cannot be anywhere. Can the universe be in Boston? Can it be in the Milky Way? Places are in the universe, not the other way around.
Is the universe then unlimited in size? No. Everything which exists is finite, including the universe. What then, you ask, is outside the universe, if it is finite? This question is invalid. The phrase “outside the universe” has no referent. The universe is everything. “Outside the universe” stands for “that which is where everything isn’t.” There is no such place. There isn’t even nothing “out there”; there is no “out there.”