I filed yesterday and realized I did the same thing and was very annoyed about it. I plan on making up the Q1 ES tax underpayment balance on my Q2 payment. Fortunately, if you do end up owing a penalty it will be relatively small and Turbotax will automatically calculate when you enter your 2021 estimated tax payments in the software.
If you make the underpayment up in Q2 the simple formula for the penalty is :
UNDERPAYMENT AMOUNT x (NUMBER OF DAYS LATE / 365) x Interest Rate (Most recent rate was 3%)
If you are to make up for the underpayment in Q2 the penalty is under $5 per $1000 of underpayment (Based on the payment being 60 days late and assuming the rate is 3%).
If you are bored and want to know the details you can find them here: https://www.irs.gov/pub/irs-pdf/i2210.pdf
