Would a doctors negative urine pregnancy test be accurate 27 days after sex ?

It depends: It depends upon how close to the end of your menstrual cycle that it was performed. A blood pregnancy test is more accurate if there are doubts.

Pregnancy test: A pregnancy test if done accurately will be positive or negative two weeks after unprotected intercourse if no further encounters have occurred since the episode. If you had sex at ovulation, the test should be positive two weeks later. So again yes.