You didn't get the $1100 on 1040 line 30? Did she show up as a dependent on your return? A child born (even on Dec 31) is considered to live with you the whole year. Did you pick the Whole Year at the top of the drop down box?
Do you have anything on line 30? If you are missing some of the first or second Stimulus payments or qualify for more but nothing got added on line 30 then you do have to amend to claim it.
How to amend 2020 return
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439
