I know you are very scared. I never said I thought it was "not good". You are letting fear color your perceptions. I do understand. I know this panic. But I see it differently because I am now on the other side.
I think your letter is fine. But my opinion is meaningless in this situation. This is appeal letter is yours. If you feel it needs improvement, keep working. It is truly up to you. If you decide it's done, stop.
you can not through fear or panic change the outcome of this appeal. There are a myriad of factors at play in a decision, most you can not control and don't even know about. Try and do what you can. Get the letter ready to your satisfaction and turned in on time. Then comes the hard part, you have to let it go.
I know it sounds insane, but at that point, It's out of your hands. Severe Anxiety ain't going to change the outcome. It will only change your mood, health, and stability. Try and remember that no matter what the dean of your school decides, you really will be okay.