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Clipping is caused by excessive gain. Your first stage on its own has gain far greater than 10 V/V, and so does the second. Other complications: the second stage is loading the first; the 2N3904 is rated for only 350mW;the Cs in parallel with 180 and 100 are giving a strange frequency response; the 10k variable looks unlikely to give unsatisfactory volume control; the 8 ohm speaker reacts with the 10 uF to form a high-pass filter.
The 10k and 1.8k at the base of T1 are unnecessarily low, replace with say 100k and 10k. Reduce the high first-stage gain by negative feedback--remove the C across the 180, which should now be about 12 ohms to get a gain of 10 (maybe you vary the 12 as volume control).
The capacitor between C of T1 and B of T2 needs to be bigger, say 47uF, because we're about to make it feed into a rather low impedance.
The second stage should be an emitter follower, based on a power transistor e.g. TIP29. Remove the 1k, replace the 5.1k with 1k, replace the 560 with a short, and the 100 with 10 ohm (or just use the speaker itself instead). If the TIP29 heats up use a heatsink. 1 watt into the speaker is not negligible.