Hello JRZ126,
I think that if you place a trimmer on the feedback, you can only make the power supply to see less voltage, so it will try to increase it. No good.
1) Have you tried to load a little the supply, e.g. with a resistor? If you tested it with no load or very light load, this could be the reason why you get the excess 0.5V. Some power supply tend to go higher in output voltage when too lightly loaded.
2) I do not know this brand of power supply, but there could already be a trimmer, inside the circuit, to adjust the output.
Good luck
Ezio