IIr filter layout to formula problems
I won't tell you if it's correct but I'll show you what it should be: -



Don't forget the minus signs on the "a" coefficients. It was taken from here.

There is the form that uses \$Z^{-1}\$ - it would make the first formula in the picture this: -

\$y[n] = \omega[n]\cdot(b_0 + b_1Z^{-1} + b_2Z^{-2})\$ and from inspection you should recognize the \$\omega[n]\$ is the output from the summer to the left. Hope this helps.