Another thing to consider is: Did you measure it under load?

A transformer usually specified under full RESISTIVE load. So, when unloaded the voltage increases by the specified regulation figure. I guess you tested it unloaded in which case you are safe. Calculating the output voltage of a transformer/rectifier under mixed capacitive and resistive load is by no means easy. For a one off, your approach of try it and see is the best way.

Russell.