Yes. If it was checked under Other Dependents and not for the Child Tax Credit that was wrong. You answered a question wrong. You need to amend your return. You should get the $1,100(500+600) Recovery rebate credit on 1040 line 30 unless your income was too high.
A child born (even on Dec 31) is considered to live with you the whole year. So you should have picked the Whole Year at the top of the drop down box when you entered your baby.
How to amend a 2020 return
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return/00/27439
And See this post
https://ttlc.intuit.com/community/file-with-turbotax/discussion/child-tax-credit-vs-credit-for-other...
