Space time is curved so there is no boundary or edge. Google it.You are right we couldn't possibly have any data to support this. All we have is our little universe small u.
Yes our universe began. Yes it did. And it was very small surrounded by what you would call nothing. And our universe expanded into nothing. It continues expanding in to that nothingness. Where's the edge? It's unknowable. But it's probably infinite just like your god.