Why such the large percent error?

This is for a physics lab on conservation of moment and the moment of inertia. The experiment is pretty straight forward. I believe I have done all my calculations correctly, but I have a very large percent error between my experimental values and theoretical values. In the experiment, we were told to eliminate ALL frictional forces from our equation. I have a hunch that this may be the reason for the large discrepancy in the margin of error, but I cannot find any information online that plainly states that this is the reason for the error. Please see the attached document. The goal of the lab is to calculate the experimental value of the coefficient κ and compare it to the accepted value for a small, solid sphere which is 2/5. The lab report is not final by any means, but this is what I have so far. Insight to my problem and suggestions are needed and welcome!