In the Layout settings, the 'has margin' option currently does not function as intended. Even when disabled, the page still displays margins.
Here is a quote from Looker Studio Help: Has margin shows or hides the margin area surrounding the report. Hiding the margin makes the report appear to occupy the entire window.
Description
Here is a quote from Looker Studio Help:
Has margin shows or hides the margin area surrounding the report. Hiding the margin makes the report appear to occupy the entire window.