I believe it is correct to play the song completely through one time only, and on the repeat, end at the fine (A B A).
There is no theoretical need for the repeat signs when DC is used, but they are a courtesy with the written DC al Fine command conveying the actual playing directions.
NWC plays back correctly. If the DC al Fine is placed immediately before the Master Repeat Close, then NWC never reads the Master Repeat Close because it does the DC before it gets to it, and stops at Fine.
This layout will play back A B A and is "correct:"
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Treble
|TimeSig|Signature:2/4
|Key|Signature:F#
|Tempo|Tempo:300|Pos:10
|Bar|Style:MasterRepeatOpen
|Text|Text:"A"|Font:StaffItalic|Pos:16
|Note|Dur:Half|Pos:-2
|Bar
|Note|Dur:Half|Pos:2
|Bar
|Note|Dur:Half|Pos:-2|Opts:Stem=Up
|Flow|Style:Fine|Pos:10|Justify:Right|Placement:AtNextNote
|Bar|Style:Double
|Text|Text:"B"|Font:StaffItalic|Pos:16
|Note|Dur:Half|Pos:0
|Bar
|Note|Dur:Half|Pos:2
|Flow|Style:DCalFine|Pos:16|Justify:Right|Placement:AtNextNote
|Bar|Style:MasterRepeatClose
!NoteWorthyComposerClip-End
If you want to play A B A B A, and still only write one version of the tune, use a 1st and 2nd ending:
!NoteWorthyComposerClip(2.0,Single)
|Clef|Type:Treble
|TimeSig|Signature:2/4
|Key|Signature:F#
|Tempo|Tempo:300|Pos:10
|Bar|Style:MasterRepeatOpen
|Text|Text:"A"|Font:StaffItalic|Pos:16
|Note|Dur:Half|Pos:-2
|Bar
|Note|Dur:Half|Pos:2
|Bar
|Note|Dur:Half|Pos:-2|Opts:Stem=Up
|Flow|Style:Fine|Pos:10|Justify:Right|Placement:AtNextNote
|Bar|Style:Double
|Text|Text:"B"|Font:StaffItalic|Pos:16
|Note|Dur:Half|Pos:0
|Bar
|Ending|Endings:1
|Note|Dur:Half|Pos:2
|Bar|Style:MasterRepeatClose
|Ending|Endings:2
|Note|Dur:Half|Pos:2
|Flow|Style:DCalFine|Pos:16|Justify:Right|Placement:AtNextNote
!NoteWorthyComposerClip-End
With this, there is no need to make two versions of the song. If you ever want to add to it or change it, you only have to work on one file, instead of making sure your changes are made in a second file as well.
Instead of the first and second endings, you could just write a (text) note to the musician telling him/her to play the piece all the way through twice before DC al coda. The musical notation is more concise, though, and allows musicians who don't read the English to understand your intentions.