Gcse arabic writing and speaking

I'm wondering how important spelling is in Arabic writing gcse. I'm making very frequent errors in spelling but have the right words (my mom can understand most of it but idk if that's just becuase she knows the way in which I speak). Has anyone have any information about how much this will effect my marks. Tbf I'm trying to gain more marks in the other papers as I know this is my weakness.

Also, is it a problem if I ocassionaly slip in to my original dialect, rather than the modern standard Arabic in the speaking exam?