If you have an existing session, and try to attach to that, no you can't--at least not as far as I know.
You firs type screen
Then, in screen, you begin an rtorrent session
The rtorrent program should start doing it's thing. This is a NEW rtorrent, not one that was running before you ran screen.
Now you do ctl+a+d
The screen should detach. Now if you do screen -r it should reattach.
So, from the top.
You do NOT have rtorrent trying to fetch perfectly_legal_linux_iso.torrent.
You now open screen with the command
Now, in this terminal, you type
Is screen terminating when you do that?