2 month old behind on development

Hallie • Had an ectopic in November 2015. Baby boy born March 14 2017 & Baby girl born March 19 2020.
My pediatrician said my son is a little behind on his development at 2 months old. She said not to worry but obviously I'm very worried. My family & friends said that he seemed advanced, so I was kind of shocked. What are some things your two month old is doing? I would like to compare to see what he doesn't do that others are doing.