yes pay now. paying sooner rather than later will reduce any penalties you may owe. if your paying online using IRS Direct Pay website select estimated tax payments.
when it comes time to file your return penalties, if any, for underpayment of taxes will be computed automatically unless you ask the IRS to compute them. you also have the option of using the 2210 annualized income method if that produces lower penalties (assuming you have them)
you won't have underpayment penalties if the tax you owe after subtracting withholding is less than $1000
also no underpayment penalties if withholding and timely estimated tax payments are 90% of 2020 tax or
100% of 2019 tax (110% if 2019 adjusted gross income over $150,000)
one of the questions TT will ask is did you make any estimated tax payments. you'll need to enter the date and amount.
