underpayment penalty

Why is turbotax calculating a small underpayment penalty when I paid the IRS directly over 110% of my last year tax due?  my AGI is over $150,000 married filing jointly but that is only due to a roth conversion in the fourth quarter. 

I have entered the payment to the IRS in turbotax as other tax payment since it was not as estimated quarterly payment.

 

how do I get rid of the underpayment penalty?