I'm not sure that I mentioned before or not, I'm not an outgoing person, it's quite opposite, I'm totally an introvert person! = I'm not sure if I mentioned before or not, but I'm not an outgoing person, it's quite the opposite, I'm totally an introvert person! 
So I prefer to spend time alone, or with my sister in my freetime. = free time
And when I hang out with my friends, I prefer to meet in my hometown, not seoul. = Seoul
I really don't like to go the crowded places, and If I go to some crowded places, like gangnam or hongdae, I feel wiped out. = I really don't like to go to crowded places, and If I go to some crowded places, like Gangnam or Hongdae, I feel wiped out.
Anyway, so I usually meet my friend in my hometown, and go to some small pubs or cafes.
And especially I really love to go hangang river park, and have picnic, or ride a bicycle, take a nap, etc.
But, I like to do some activities, emm, I can say I'm not an outgoing person, but I like to do some active things.
So, I like to play tennis, bedminton, all kinds of activities which use ball! = badminton 

Note: You should capitalize the names of countries, nationalities, and languages because they are proper nouns—English nouns that are always capitalized.