Hi,
You're OK so long as you aren't hearing any distortion. If the amp goes into current limiting, then the overall power output is reduced so it could clip (distort) more easily.
You won't hurt anything because the amp's protection circuit would normally shut it down if the output transistors got too hot. All protection circuitry usually has thermal monitoring to shut down the amp if the output stage overheats.
Measuring real-time power output levels is really difficult because of the constantly varying music signal, so you'd want to know what the peak values are. In some ways, it would be easier to put an oscilloscope across the amp output signal and monitor the waveform for any evidence of clipping. You can see that when the top and bottom of the waveform is truncated. If that occurs, I expect you'd hear the distortion because it would be in the 1% to 3% range (at least), which is pretty audible.
Regards,
