I would say your reach back could the most work.
If you see the attached images reach.png is the furthest you reach back. Notice arm is bent at elbow, you are looking over your shoulder towards target I assume and you are perpendicular to the target.
Try have a more loose run/walk up and to move the lower part of your body more. On walk up, take your right shoulder blade and have it look directly at target. Do not look over your shoulder. Instead, look towards the back of the teepad where your straight arm should be extended back with disc. Takes a while to be comfortable and not see exactly where you are throwing but you can get it.
Now release.png is your release. Looks like your weight is behind your plant foot. Maybe try getting more weight on the lead foot.
Follow.png shows the extent of your follow through. I exaggerate mine and for RHBH come pretty much a full circle and have my left foot land ahead of my right/plant foot.
This is my advice. I cannot claim that this will work for you nor for anyone else. I am in no means a big arm, just someone who wants more people to become better.