This doesn't have a straight answer unfortunately. Germany is somewhat strict when it comes to dual citizenship, and generally they'll make you choose when you reach adulthood and your parents have seperate nationalities. But there are exceptions, like if you've lived in Germany for long enough, or of the second nationality is EU/ Swiss

There might be more that I missed at first reading, but I think none apply to you. The "Optionsrecht" (Right to choose regarding multiple citizenship) might have defaulted to US because you didn't apply before adulthood, I'm not sure. But in that case you could reapply, because in theory you automatically had German citizenship at birth.

I don't see a way for US/DE dual citizenship though.