Jez I think you did fine.
As Grainger said a number of airfields advise position reports if flying in after the tower/ info/ radio have closed.
My understanding is, without checking in CAP413, is the correct thing to say is:
xxxxxx traffic - G-ABCD position report and intentions.
(xxxxxx being the airfield name)
One evening, when flying back to a certain airfield, this proved V useful for me as I discovered another a/c in similar position and height - so I let him descend first until we were visual.