Hi Angeline,
Nice to see you Angeline, and what a lovely name. Where are you from? Your level of English is already very good, so the changes I make to your passages will mostly style. I hope they help

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My favorite number is 7 because I was born
on April 7
th and there are
also so many significant events related
to the number 7. One of these was when I ranked number 7 during high school graduation and another was when I crowned Ms. United Nation
and my candidate number was 7.
You would probably also need to explain more about the Ms. United Nation crowning, in order for people to know whether you meant the actual UN or an alternative version of it. Where was the ceremony held, for example? And, how were you ranked number 7 in your high school graduation? For what ability? (please excuse my lack of knowledge about this as we don't have such as ceremony in the UK)