There is no hard line between this is thick enough and this is too thin and will blow up.
A thinner track just has more resistance, so it has more losses at a given current and gets hotter at a given current. At some point the losses can become so large that the track itself gets hot and starts heating near by components. But what is considered as a track getting too hot also varies wideley depending on the ambient temperature, how much heat the components can handle, how much heat the PCB can handle etc...
For currents under about 3A people tend to well overestimate how thick of a track they need, even a fairly wimpy thin looking track will handle that fine. But past that, then that the pesky square in the P=I^2*R starts to take over and the power loses really start growing quickly with each extra amp. Its at about 10A where you start needing big thick fills of copper. and at 20A the thicker 2 or 3 or 4 oz copper PCBs become sort of a must have.
With the sort of powers your amp runs at it probably doesn't need hugely thick copper, but its hard to say without a picture of what you find as thick. Audio amplifiers also have an advantage that they don't tend to output max power for very long in real world use cases, so they tend to run a lot cooler than what the worst case math predicts.