After the list of real property, with the appraised benefits as approved by the court, or that part thereof from which no appeal is pending has been filed with the secretary of the district, then from time to time, as the affairs of the district demand it, the board of directors shall levy on all real or other property upon which benefits have been appraised, an assessment of such portion of said benefits as may be found necessary by said board to pay the cost of the execution of the official plan including superintendence of construction and administration, plus ten percent (10%) of said total, to be added for contingencies, but not to exceed, in the total of principal, the appraised benefits so adjudicated. The said assessment shall be apportioned to and levied on each tract of land or other property in said district in proportion to the benefits appraised, and not in excess thereof and in case bonds are issued as provided herein and hereafter, then the amount of interest, which will accrue on such bonds, as estimated by said board of directors, shall be included in and added to the said assessment, but the interest to accrue on account of the issuing of said bonds shall not be construed as a part of the cost of construction in determining whether or not the expenses and costs of making said improvements are or are not equal to or in excess of the benefits appraised. As soon as said assessment is levied, the board shall report it to the court for confirmation. Upon the entry of the order of the court confirming the assessment the clerk of the court shall transmit a certified copy of said order to the governing or taxing body of each political subdivision assessed and said governing or taxing body shall receive and file the same. After the court has confirmed the assessment, the secretary of the board of directors, at the expense of the district, shall prepare in duplicate an assessment record of the district.