An extension has to be filed by April 15, 2019 so it is too late to file an extension. An extension only extends the time you have to file your return, it does not extend the time you have to pay taxes. Taxes not paid by April 15, 2019 will incur a penalty & interest until the taxes are paid in full. Since your are only a day late your penalty & interest would be very little. The IRS (& State) will send you a letter letting you know how much you owe.
