I have a 3x12 matrix I'd like to input into my LaTeX (with amsmath) document but LaTeX seems to choke when the matrix gets larger then 3x10:

\begin{equation}
\textbf{e} = 
\begin{bmatrix} 
1&1&1&1&0&0&0&0&-1&-1&-1&-1\\
1&-1&0&0&1&1&-1&-1&0&0&1&-1\\
0&0&1&-1&1&-1&1&-1&1&-1&0&0
\end{bmatrix}
\end{equation}

The error: Extra alignment tab has been changed to \cr. tells me that I have more & then the bmatrix environment can handle. Is there a proper way to handle this? Also it seems that the alignment for 1's and the -1's are different, is that also expected of the bmatrix?