user535918, The datasheet only specs a maximum guarantee of 3 A. It touts 4 A in the headline. But if you look at the spec, the guarantee is only 3 A. You will need to support 3.2 A into a 4 Ohm load to get 20 W. So the
at least specification already fails. Also, the amplifier is only guaranteed stable at gains of 10 or greater. If you have to accept 1 V rms input and are generating 8.94 V rms at the output, that's less than a voltage gain of 10. Might be yet another issue there.