There are optimists, pessimists, and realists. Optimists will say that everyone matters, despite all your flaws and problems. Pessimists will say nothing matters at all. A realist will break it down for you. In the grand scheme of things, when it comes down to it all and you're looking at the whole universe, no, you don't matter. Nobody matters in that sense. One tiny person, on a tiny planet, in one of the 200 billion galaxies in our universe, won't matter.
The average human has a lifespan of 79 years. It seems like a lot, and on our scale, it is. Compared to the 10 billion years a star with the same mass as our sun can live, it seems like a millisecond. So, technically and realistically, we don't matter. Neither does our planet, or even our solar system. For all we know, there could be a billion planets in our universe that harbor life like us, each with over seven billion creatures. Pessimistically speaking, nothing matters.
Now before you succumb to an existential crisis and curse my name for making you feel small and unimportant, think of it like this. The universe is the big picture. We, here on earth, are the brush strokes that make up the picture. So, maybe we are unimportant to some, and the big picture is all that matters, but we are literally what make up the picture. It would be completely different without our brush stroke.
So, when you're thinking you're a waste of space, remember that you physically can't be. There are stars that are 100 times the size of our planet, and they aren't wasting any space. There is plenty of room for you.
When you are thinking that you are unimportant, that maybe you don't matter to the 700 billion possible aliens out there, remember you matter to your family, community, country, and your earth. One single person can't begin to alter the universe, but you can change a person's life and make the world a better place. Your everyday actions matter, whether you decide to get up and go out or stay in bed and sleep the day away. Your votes matter, and can change the way we treat our environment and ultimately our planet. Your smile matters, and can twist a person's bad day into a good one. Your words matter and can affect hundreds of people at a time. Everything you do on a day-to-day basis matters, and you should keep that in mind.
As the great Carl Sagan said, "The cosmos is within us. We are made up of star-stuff. We are a way for the universe to know itself."