Your question is one of the great questions of life and one philosophers have pondered for centuries. What is the meaning or purpose of life? Based on how the question is related there is a very important aspect of the argument that is not properly addressed. Although the universe is immeasurably large, the scope of influence must be applied to properly analyze human behavior. The question assumes the scope of human influence includes stars, planets and galaxies outside our own. That premise is incorrect. The scope of human influence is relegated to Earth. Humans have explored outside of Earth, but there is no evidence of intentional influence that has altered the course of anything. For example, when Neil Armstrong walked on the moon it did not alter, influence or otherwise change the moon or how it interacts with the Earth. Interaction does not equate to influence.
The scope of influence is limited to Earth and even then the scope is further limited by actual influence versus interaction. It can be impossible to determine on an individual basis the difference between actual influence and interaction. If you meet someone on the street and each say hello, that may be an interaction. However, if that meeting causes the person to not commit suicide then it is influence. Such connections can be difficult to analyze. These are connections on the micro level of human connection.
Connections at the macro level include world leaders, inventors and other infamous characters whom have had a measurable impact on society. George Washington, Martin Luther King Jr., Henry Ford and Al Capone have influenced society because of their exploits. Did any of their actions affect a large portion of the universe? No. Did it have an impact on their scope of influence? Yes.
The point is simple. One person cannot influence the universe because the scope of influence is too large. One person can alter the course of human history. Does it matter in the universe whether you are a decent person? No. Does it matter to your family or a stranger? Yes. The individual scope of influence varies according to the actions you take and the connections you make. There is a point where nothing you do matters on a universal level. The flip side is that all those billions upon billions of stars don't have influence over you either.