The retirement savings contribution calc. says I qualify for a credit of $2,000, but can only take $473 because I don't owe enough. But TT says I owe $2121! WTH?

I don't understand why TT is limiting me to taking only a $473 credit of my $2000 RSCC when I clearly owe more in taxes than $473, per the "Federal due" calculator in the upper-left corner.