The final passage of any ordinance under the provisions of sections 88.107 to 88.127 shall be deemed a conclusive determination that the amount of the assessment therein made is in conformity with section 88.117 and that each lot or parcel of land within the assessment district by such ordinance defined has been benefitted by the improvement in question in an amount at least equal to the assessment charged against it by such ordinance, plus all credits to which it is entitled under section 88.113.