Oh Ana Maria!!
I know just how you feel.
I did exactly the same thing - a waffly case, over-emotional letter, hunting for feeble mitigating circumstances, shaking with nerves during the hearing, nearly burst into tears...
Most frustrating of all, if I had only dug a little deeper for academic evidence, it was all there in dollops.
If only I had known then what I know now, not only about how to present a case, but how there is life afterwards for me and my son!
Not everyone will win their appeal, but if you follow the advice on this forum, especially from Etienne, you really will have a better chance. And when nerves and high emotion threaten to take over please remember, this is not a matter of life or death. As someone said to me last year on this forum, wherever your child ends up at school, "Cream will always rise to the Top".