A general inertia matrix has 9 entries: three moments of inertia and 6 products of inertia. You are only introducing the moments of inertia about the x and y axes. Where are the other entries? Is the link assumed symmetric? Depending on the symmetry you can reduce the inertia down to the three moments of inertia but since you have no Z inertia at all this seems problematic. I'd prefer you to add all of the inertia tensor entries here and then if you assume symmetry about various planes you can set the appropriate products of inertia equal to zero when you get to the numerical simulation.