6.q12 was really bad; 11.q13 was the obvious response. Also, white did better to spread out across the board, while my first few moves were all in a narrow band across the center. Maybe |6.q19 for a better idea?
I agree that 6.q12 was not the most fortunate move, I think. 12.r20 might indeed be better. The (4,5) connection with n15 is not easily passed by white, and it's close enough to the right border. Either you would succeed in connecting n15 with r20, or you would make a connection to the right side above row 16.
But I think that the point where the game pivoted was 12.q8.; the obvious following 13.p11 voided that move and gave white an advantage. A better alternative line would be: |12.q1913.o1814.n2015. q1716. p2117.m1918.l19 and black has a strong position from there.
But I think that the point where the game pivoted was 12.q8.; the obvious following 13.p11 voided that move and gave white an advantage. A better alternative line would be: |12.q19 13.o18 14.n20 15. q17 16. p21 17.m19 18.l19 and black has a strong position from there.