If this is your first swing test, I would like to offer a few more tips.
Use as much string as you can manage without dragging your model rocket on the ground when you start and stop your swing test. You will get more speed and a smoother path.
If your rocket is marginally stable a swing test may be inconclusive----the rocket may tumble around and not point forward very much. Kind of hard to tell the difference between slightly stable and totally unstable.
I would strongly recommend that you follow the insertion of clay (at the tip of the nose cone) with a layer of epoxy. Belt-and-suspenders, and all that.
An alternative check: have you ever heard of the cardboard cutout method of determining center of pressure? Find the center of gravity by balancing the model on something (make sure the rocket is loaded in flight condition, with wadding and motor). After noting the location of the C.G., find the center of pressure by making a cardboard cutout of the profile of your rocket and balancing that cardboard piece. The pivot point of the cardboard represents the lateral (or, 'from the side') centroid of the area, and is usually a conservative estimate of the C.P. If the C.P. is one to two body diameters behind the C.G. then you are probably OK.
