What is the ruling concerning the breast augmentation surgery I underwent at the age of 17 without knowing it was unlawful, and it was not for the purpose of augmentation but because my breasts had not developed?

If a trusted physician determines that the breast will not grow and will remain like a child's breast, and this is considered a visible defect or an impediment to breastfeeding and the like, then there is no objection to performing this surgery, as it falls under the category of treatment, not beautification. What is forbidden is seeking beautification, as it involves altering Allah's creation.