Such petition shall be filed with the clerk of the county within which the district is to be formed, who shall within fifteen (15) days examine the signatures thereon and certify to the sufficiency or insufficiency thereof, and for such purpose the county clerk shall have access to all registration books in the possession of the officials of any municipal corporation in such proposed port district. If such petition be found to be insufficient, it shall be returned to the persons filing the same, who may amend or add names thereto for ten (10) days, when the same shall be returned to the said clerk, who shall have an additional fifteen (15) days to examine the same and attach his certificate thereto. No person having signed such petition shall be allowed to withdraw his name therefrom after the first filing of the same with the said clerk.