Yes, you can make the payments online and you can make additional payments.
Per IRS: You may send estimated tax payments with Form 1040-ES by mail, or you can pay online, by phone or from your mobile device using the IRS2Go app. You can also make your estimated tax payments through your online account, where you can see your payment history and other tax records.
For more information check: IRS.gov
As for the state, which state return are you filing?
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