If any person protests against the extent of the district, or against the inclusion of property in the district, the board of supervisors shall have power to make such changes in the boundaries of the proposed district as it finds to be proper and advisable. The board of supervisors shall establish the boundaries of the district in accordance with its findings, but it shall not extend the boundaries of the district, nor shall it modify the boundaries so as to exclude from the proposed district any territory which will be benefited by the improvement. Any territory which in the judgment of the board will not be benefited by the improvement shall not be included within the proposed district.