2020 baby and 3rd Stimulus

I filed our 2020 taxes mid February and they were accepted. My husband and I claimed our son and our new baby who was born in 2020. Our AGI is well below the limit and I calculated that I should be getting $5,600 with the 3rd stimulus. $4,200 is pending for deposit which leads me to assume the government went off our 2019 taxes and didn’t count our 2020 baby as a dependent. What can be done?