Thank you for posting your question here, I will try to answer it to the best of my abilities.
Usually you're supposed to take two pill in order to make up for the missed one, that's what I've been told by most doctors.
The smart thing you did was taking the emergency pill on the next day,ellaone
can be taken upto 5 days after having unprotected sex, so since you were just over the 3rd day, it should've worked.
Now what you need to know is that ellaone had been shown to stop 60% of all cases, so its not 100%.
But since you're home pregnancy
test has come out negative after waiting for 3 weeks, it is highly unlikely that you are pregnant, to be 100% sure, you can take another home pregnancy test tomorrow.
I hope this answered your question.