Form 2210: avoiding underpayment penalty

I paidmore than 110% of my 2021 tax total, however, TurboTax is telling me I have $118 underpayment penalty. Why?

Details: I had large long-term capital gain in May. I paid a single estimated payment by June 15 to ensure I would achieve the 110% safe harbor threshold, but it's still listing a penalty. How do I fix this?