How can the Universe be limited or unlimited?

I doubt anyone would know the answer to this question, but I'm going to ask it anyway. If scientists believe the Universe is expanding and is limited. What's at the end of the Universe and what's beyond that. How is that possible? But how is something unlimited, it kind of reminds me of computers, in a glitched level in a video game i tested, i went over an edge and I kept falling forever. Could the Universe work the same way? If the Universe can be infinitely big, than something can be infinitley small. No matter what, something can be smaller than even the smallest things in the Universe. Does the Universe work the same way? How did scientists ever come to the conclusion that the Universe is limited and expanding? It can't make sense, cause what's beyond the wall that is the edge of the Universe? It's too confusing, and if someone can simplify how those parts of the Universe work? Thank you