Does $\textbf{PCP}[poly(n), O(1)] = \textbf{coRP}$?
Recall PCP theorem, $PCP(log(n), 1)$ is NP already and actually $PCP(poly(n),1)$ is $NEXP$.

The problem of your proof is that you cannot simulate a coRP algorithm on a string with length only $2^q$. Though it will only access q bits, the bits it accesses to depend on the random coins. You should not think of a specific coin outcome but all of them on a input. That is basically why your proof doesn't work.