If you have mentioned weight of the baby it would have been helpful. Anyway 2ml extra should not cause any danger symptoms. Salbutamol will have range of dosage. if its within the range there should not be any problem. Look for any new symptoms and meet your pediatrician if anything abnormal. Dont give the next dose or stop medicine for one day. If required give only salbutamol nebulisations. But give under pediatrician's guidance.
Next Steps
If any new symptoms contact your pediatrician.
Health Tips
Keep prescription beside medicines and see the dose every time before giving it.