HP PRINT SERVICE PLUG IN. Set to print to 6 x 4 photo paper but it doesn't, why?

[AC Question]

HP PRINT SERVICE PLUG IN. Set to print to 6 x 4 photo paper.

I have:
HP Envy 4500e
Galaxy Note 3. Android 5,
HP Print Service Plugin.
I load 6" X 4" paper in printer and select 6" x 4" paper size in the app.
Whether I choose Portrait or Landscape photo I can't get to print 6" x 4".
I get print but only 4" x 3" in middle of the 6" x 4" paper.
Any advice please ?
Thanks