Private Adoption in the Philippines

hi.. im filipina,single. someone's new born baby give it to me but did not go for legal procedures..only promisory note that giving up her child. she give birth in a hospital.. give the baby other name under her.. but i register the child birth certificate under my name as a mother.. but now the child is already 3 years old but the biological mother and relatives suddenly show up to me and saying that they want the child to take back.. i don't know what to do now.. im afraid to be separated in that child we love and cherished her already..