I failed my driving test for stupid reason

If the light doesn't turn red before you clear the intersection it shouldn't be a problem.

 

You can brake to slow. But once you have slowed your new slower speed AND your old gear selection may or may not put your engine RPMs too low. If so, you downshift. Not many drivers are going to know the road speed & gear choice.

You failed the road test. Whether it was fairly or unfairly is beside the point unless 1) you plan on telling the next road examiner you were unfairly failed, and 2) you think telling the 2nd examiner this info will cause him to pass you on test #2. Nobody wants to hear why you did A, B, or C. Just do the right thing at each part of the test. The reason for an action is irrelevant.