wrong date of marriage on my 2 child's birth certificate

just wanna know what are the procedures in correcting the wrong entries on my child's birth certificate? me and my husband got married last june 2006 at the city hall of pampanga. then we had our church wedding last december same year as on our civil wedding. i gave birth on my 1st child last july 2007 and my husband was the one who accomplished the birth certificate of my son. instead of putting june 2006 as our date of marriage, he indicated december 2006 was our date of marriage. our civil wedding date was the one registered at the nso. we discovered it when we request a copy of authenticated marriage certificate a month after giving birth. we didn't know that it will be registered since that we know our civil marriage is just a "secret" marriage. later on, we find out that there is no such as "secret marriage". we've learned from this mistake. will it be costly if we correct the wrong entries? please help. thanks a lot.

File a petition for correction of entry. This NSO site will be a great help ----> http://nso.citizenservices.com.ph/nso-certificate-correction

Good luck!