If you're playing it as an open chord on a guitar then it'd look like this:
[attachment=161669:GMaj7.pdf]
That goes B, D, G, B, F# (3rd, 5th, root, 3rd, 7th)
In the same position it could be played:
[attachment=161671:GM.pdf]
which goes B, F#, G, B, G (3rd, 7th, root, 3rd, octave root)
and still be a G∆/B (the 5th isn't as important as the other notes, so is often the first to go when simplifying chords)
ultimately, if it sounds right, it is right.
(these files get changed to some crazy heathen format by bass chat, just change the extension to .pdf and they'll open in adobe as normal)