For a near-100W amplifier, Bertus gave you a good link on your other thread. If you really want to use the one you originally posted, I'm sure one of us could redraw the schematic in a more conventional fashion and correct the mistakes.

 

R11 is the volume control. To eliminate the clipping then simply turn down that volume control.
R12 is the 8 ohm speaker but you have its ground end connected to the B input of the 'scope instead of to ground. The other end of R12 is where the B input of the scope should be connected.

The Darlington output transistors must have pretty large heatsinks to avoid damage from overheating.

 

I didn't see that on the schematic.

The waveform indicates that both positive and negative peaks of the signal are being clipped symmetrically. This would suggest that the circuit is working correctly but it is being over driven by the input signal which is too large.
As I suggested in my first post, you can reduce the amplitude of the incoming signal by adjusting the volume control, R11 until there is no more clipping.
From the symmetrical nature of the displayed waveform, I am assuming that you have both the positive and the negative power supplies connected correctly.

 

Thank you guys so much! I got it. I'm now working on my first amplifier project. Wish me luck!

 

Thank you guys so much! I got it. I'm now working on my first amplifier project. Wish me luck!

Good luck. Be careful.