Since it's very hard, if dang near impossible, to get a Catholic answer on this, I think the musings of a couple priests will have to suffice.
Bullet point one
Either I or my wife asked a priest once how long Adam and Eve stayed in the garden of Eden and he said it was only a few hours, long enough for Adam to name everything, take a nap, get major surgery and for God to create Eve. So clearly if they were supposed to stay there forever, they didn't even come close.
Bullet point two
Paradise (i.e. the Garden of Eden) might not be the "Walled Garden" from the Song of Songs.
Paradise is a relationship! Notice that St. Paul when he was taken up to paradise doesn’t talk about what he saw. He talks about what he heard. Paradise was a fairly common word beyond its religious use. There were lots of “paradises.” Paradise was originally an Iranian word that meant a walled enclosure. It came to mean the garden in which a king could walk with his friends without the formality of the court in which his every word was law. It was a place of friendship, of intimate conversation. In the Bible it came to mean the garden of Eden where God walked in friendship with Adam and Eve. Paradise is about the relationship, not the real estate. In effect, Jesus said to St. Dismas, the good thief, “Today you will walk with me in my royal enclosure as my friend.”
Reverend Know it All
so you may ask how an Angel could guard a relationship, and I can't answer that.
But, I think the answer is yes, we were to remain in a close relationship with God if not for the Fall, but no we weren't supposed to necessarily remain in one walled garden.