You are actually not late. The deadline is today, May 17, 2021. So, there is more time to see if it is accepted through electronic filing before you have to consider filing by mail.
If you do need to file by mail, getting a postmark of May 17 is considered a timely filing.
Take a look at the following TurboTax article and the ones linked at the bottom of the article for more advice about what to do next:
What if I e-filed before May 17, but my return got rejected after the deadline?
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