Palestine was a land defined by international borders. It had a native population who were citizens of Palestine.
The mandate owned no land and had no borders of its own. It held the land in trust while "rendering of administrative advice and assistance by a Mandatory until such time as they are able to stand alone." ~ LoN covanent
There has been a lot of misinformation about the mandate but it was assigned to Palestine to bring it to independence.
'To bring it to Independence'
Which they rejected in 1947.
No they didn't.
They rejected the partition plan. The partition plan would have brought them independence.