Paid $68 to the state in original return. Now making an amendment, state tax withheld updated from $843 to $743, amount due $100. Why I pay more for a lower total income?

For now the State amended return total payments and credits shows $811 (which is 743 68). Shouldn't it be 743-68 because I already paid $68?
Also what should I put in "Overpayment as shown (or adjusted) on original return"?