Giving formula for those first five days while your milk was still coming in doesn't cause any lasting problem for your baby. Delayed milk production in the first week is common, especially after a C-section or a difficult delivery.
Next Steps
Keep breastfeeding or pumping frequently now that your supply has started, since frequent removal is what builds and maintains it. Track your baby's weight gain and wet nappies to confirm feeding is adequate.
Health Tips
If your baby still seems hungry after feeds or isn't gaining weight well, please see your paediatrician to check the feeding plan.