Simple, yet somehow complicated experiment.

Ok, i am gonna be honest. I cant find a mistake in my work, so i hoped someone would lend me a hand. I am trying to do a simple experiment on conservation of energy. I am putting a soda can on the top of the ramp. Then i release it, while filming. Then i derived a formula for calculating coeficient k of moment of inertia, which only used time, vertical dostane, horizontal distance and some constants. The problem is, the results are way off. I tried to use different angles, cans (size, empty/full), time measurement device but nothing seems to help. Any ideas?