Emotional-Will-6859's journey

I recently found myself in a tough spot after getting fired from my corporate job. Just a few days later, I had a final round interview at a new company and, feeling a bit nervous, I talked as if I was still employed at my previous job. To my surprise, I received an offer, but now I'm anxious about the upcoming background check. I'm unsure how to handle this situation. Should I be honest about my final day at my old company? If HR asks why I'm no longer there and why I didn't mention it during the interviews, what should I say? I'm considering a few options for the background check: 1) Enter the correct termination date and hope they don’t catch it, 2) Change the date to a week later than when I was actually fired (since the interview was just four days after my termination), or 3) Claim that I still work there (though I'm hesitant about that one). I really appreciate any advice on how to navigate this tricky situation!