Active transport of Ca2+ ions against chemical and electrostatic gradients, assisted by ATP hydrolisis
At equilibrium, the entire process (transport of $2~\ce{Ca^2+}$ ions and hydrolysis of $1~\text{ATP}$) involves no change in G.  

\begin{align}
0 &amp;=\Delta{G_\mathrm{total}}\\[2ex]
0 &amp;=\Delta{G_\mathrm{ATP}} + 2\Delta{G_{\ce{Ca^2+}}}\\[2ex]
0 &amp;=\Delta{G_\mathrm{ATP}} + 2\Delta{G_{\ce{Ca^2+},\text{ concentration gradient}}} + 2\Delta{G_{\ce{Ca^2+},\text{ electrostatic}}}\\[2ex]
0 &amp;=\Delta{G_\mathrm{ATP}} + 2RT\ln\frac{C_\mathrm{in}}{C_\mathrm{out}} + 2ZF\Delta \Psi\\
\end{align}

So basically I'm saying you made two mistakes, one a sign error and one a factor of 2 error.