I don't mind

- First year, in senior high school, - I still feel my version is better. An article "the" is missing here (first year -> the first year). Also there is no such thing here as senior high school, either middle school or high school.

==> When you kind of put pointers, you don't use "the", like "First, Second...".

- our relation of time - I really don't think this is a good expression, actually I did not get it when I first read it. I wonder if you can get a second opinion from someone else about this.

==> Unfamiliar with something doesn't mean it is wrong.

- repeat the feeling – still feel strange about it. I just tried to Google this expression, but could not found one.

==> Your can repeat anything and nothing wrong with that. It is not an fixed expresson.

- “an ethnic minority” is better than “ethnic minority”

==> It would be both necessary and grammatically wrong.  You can say "I am a man of priciple", not "I am a man of a principle".

- An smile -> a smile 

==>  An smile is your version.