Yeah, like JR stated you need to slow your motions down. You should almost walk through the motions, reach straight back, your reaching back and bending your elbow.
I don't talk about this stuff much but I will try.
Also, your final plant step is pretty wide, shorten it. Walk through the motions, and accelerate hard when the disc is entering the hit zone (your left pec). Push your elbow straight towards the target as far as you can then allow your body to open up and turn while your elbow opens as well. Finally the wrist will open and the disc will fly. These things should not happen because you forcing them to happen, but they should happen because of the movements you set in motion.
Hopefully this helps, if anyone feels it is wrong, correct me.