Needles use in those kind of places are not the same that people use to inject drugs.
In the ones used to inject drugs, the space inside remains without air, so the virus can survive longer than usual even being out of the body.
But in a normal needle like the one you got pricked with, in the case there were any traces of blood from a different person, it would have been already exposed to air, so in the remote case the person that got pricked before were HIV+, the virus would be already unable to infect.
But a transmission in the scenario would be extremely rare, if it could ever happen.
As I said, Dangerous situations are those ones in which people share needles to inject drugs with, or sanitary professionals that have accidents at their work places with needles they have previously used to extract blood from HIV+ patients.
You can repeat the test after 28 (if it's a combo duo ag/ab), but I am sure is going to be negative.
All the best.