Escape velocity $v_e = \sqrt{2GM/R} = \sqrt{2G(\frac{4}{3}\pi R^3 \rho)/R} = R\sqrt{\frac{8}{3}G\pi\rho}$. Since density $\rho$ is the same, $v_e \propto R$. If the radius is doubled, the escape velocity is also doubled: $2 \times 11 = 22$ km/s.