Do I amend my 2020 return so I can add me newborn to receive child tax credit?

Not unless your baby was born in 2020.  If he was born in 2021 you can't add him to your 2020 return.

To add to @VolvoGirl's reply, keep checking the IRS website below.  The IRS is working on a portal that will allow you to update information such as a child being born in 2021 which could make you available for an advance payment in 2020 of your 2021 Child tax credit.

https://www.irs.gov/credits-deductions/child-tax-credit-update-portal

Hope this helps.