Since you knew you had a test coming up, you shouldve picked up a THC test kit and tested yourself 3 days before the scheduled U/A.

I didn't do anything special in order to pass my test, I just assumed that 27 days was enough time to get the THC out of my system.
Bad move. Never assume. How many days a person takes to rid the body of THC depends on the persons body chemistry and numerous other factors. Never rely on "detection timetables", assumptions, and guesswork from others as they are almost always off the mark. Its your career opportunity and your future thats on the line, so periodically test yourself so you know for sure.

With those variables in mind, do you think I'm OK and it shouldn't have showed up in my urine
Nobody can give you a realistic and accurate answer to that. Each persons body is different and there are too many variables to take into consideration to arrive at a guesstimation. Only periodic testing with a THC test kit can give you that answer.