I don't think SCARM has an "auto-fill" function, but the tutorials suggest the use of flex track to close loops, etc., and that's what I usually do. I knew about the trick of adding extra track, but with angled reversing loops, 45-degree crossings, etc., making revisions gets very tedious.
Being able to move the track in precise increments with the arrow keys, and having it turn colors when it's lined up, would make things much easier.