After my study, I have came back China. In this case, I only have very few opportunities to use English. As I did make a lot effort in learing it, I do not want to lose it. Therefore, I am here to find some English speakers to practice. In return. I am rather happy to help you with your mandarin!
No offense but I don't think your English is "relatively good".
Even I have found two errors.
"I am a native Mandarin speaker."
"I have come back to China." (I don't know, but "After my study/graduation, I came back to China" sounds more natural to me.)
And "Therefore" and "rather happy"? You sound like a robot.
Seriously girl, dreaming about your language skill on a relatively good level might not help to improve.