A preterm baby is not free from complications. Especially if there has been prolonged labour or difficult extraction of the baby. But is nice to know that your baby is otherwise doing fine.
The weight gain seems alright too. As your Pediatrician
as ruled out any problem with your baby, it is unlikely there is an abnormality in the tongue .
Do remember that a protruding tongue is seen in congenital hypothyroidism
and needs to be treated as soon as it is diagnosed. But since your baby is otherwise active, the Pediatrician must not have felt so. Cereal feeds are given as weaning foods and not recommended at this age.
Encourage exclusive breast feeding for your baby for the first 6 months