It really does not matter where the GC is on the rocket. All that matters is that the CP is behind it. That means as the rocket changes angle relative to the airstream, as it rotates around the CG, that the forces on the fins will point the rocket back in the straight-forward direction. If the CP is forward of the CG then the rocket keeps trying to swap ends after it leaves the influence of the rail. Behaviour known as "skywriting" results.
Skywriting is dangerous. If things are marginal then as the motor burns the CG moves forward. At some point the rocket attains stability again (with motor still lit
) and accelerates quickly in the direction it was when that happened. This could be towards the crowd. Really dangerous as you don't have time to get out of its way.