"If you checked that box incorrectly you probably should amend your 2019 return, as it [MAY HAVE] reduced your standard deduction so you may have paid more tax (or gotten a smaller refund) than you were entitled to."
Look at line 8 of form 1040, to see how much your standard deduction was. A dependent's standard deduction is the lower of his earned income + #350 or $1100. So, it's only dependents with unearned income who may have paid more tax (or gotten a smaller refund) than they were entitled to.
