In my opinion, you're already making a pretty big assumption about the universe existing in the first place. Nothing like a good ol' ontological debate.
A couple hundred years ago, no one could imagine that Earth is round. It was beyond what they learnt so far in their life (they knew it was flat). I bet it's the same with the Universe's edge. I bet it's a simple answer, something that will make my kid's kid's kid's kid slap his forehead and say "Lol my great great great great grandfather was such a newb, thinking the Universe is infinite".