How big the universe? We have telescopes that can see back to the origins, 13.8 billion years ago. Now universal distance is measured in light-years. To reach us from the origins, light would have to travel 13.8 billion years. We can’t see any farther, so as far as we’re concerned, that’s it.
What about the light that went in the other direction? There’s no way of finding out. For us, the universe is 13.8 billion light-years long. Tell me, is that big enough for you?