Well it doesn't really matter that much, there is always a first time to everything. It doesn't matter if a person isn't terrific at something as long as they get the general idea and keep an audience well into it then it will be fine. The main thing a writer of scripts for films or whatever has to pay attention to is the intrigue and interest of the story. What makes it so great? Will the audience stay awake for the whole duration of the film?
Intrigue is something that is of great importance and shouldn't be ignored. To catch the audience's attention you have to try and make the story of the film interesting and most of all intriging so that they won't get bored and enjoy it.
I'm only an amateur writer but I thought that you wouldn't mind some advice seeing as you seem so down on yourself. You can send me the script via e-mail and I can read it and give feedback on it for you. I don't criticise other people's work so don't feel too obliged.
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VTR250