All the signature papers shall be filed in the office of the City Administrator as one instrument. Within five days after the filing of the petition, the City Administrator shall ascertain by examination the number of electors whose signatures are appended thereto and whether this number is at least equal to five per cent of the total number of voters registered on the date of the last preceding regular municipal election. If he finds the petition insufficient or irregular, he shall at once notify one or more of the committee of sponsors of that fact, certifying the reasons for his finding. The committee shall then be given thirty days in which to file additional signature papers and to correct the petition in all other particulars. If at the end of that period the petition is found to be still insufficient or irregular, the City Administrator shall file in it his office and shall notify each member of the committee of that fact. The final finding of the insufficiency or irregularity of a petition shall not prejudice the filing of a new petition for the same purpose, nor shall it prevent the council from referring the ordinance to the electors at the next regular or any special election at its option.