If you're getting a refund, there's no need to panic.
2018 tax returns that are due a refund have until April 14, 2022 (October 15, 2022 with an extension) to be filed with the IRS before the statute of limitations on the refund runs out. If you don't file by then, the U.S. Treasury simply keeps your "donation."
However, if you owe additional tax, file your return as soon as you can, even if you can't pay your tax bill right away.
The late-filing penalty can be 10 times higher than the late-payment penalty, and the longer you wait, the worse it gets.