BC550 Darlington Clipping
The voltage across C3 (9 v) fixes the quiescent current through R9 at about 10 mA, for a quiescent voltage across R9 of ~1 volt. Any negative swing less than this will reverse bias the Darlington BE junctions, clipping the output. So you can only allow a 2 V pk-pk signal at the base of Q9. The rest follows. 

And your gain is not as high as you think it ought to be because of the loading by the Thevenin equivalent of R11/R12 through C4.