came to Korea.
This is an event that is still to happen. Change your time frame reference to future tense presentation. While the reviewer will understand that you are ESL, you must make an effort to show that you can deliver correctly formatted simple English sentences.
I have international online friends and try to communicate with them in Korean or English to improve
What happened to the development of your Chinese language use with online friends? If you are not particularly keen to develop your Chinese skills, which would be a waste if you ask me, then do not include it in the list of languages that you are currently learning.
I am sure I can obtain at least TOPIK level 3.
Try not to refer to TOPIK in the essay if you have not taken it yet. You can always take the test when you complete the 6 month language course in Korea, if you are accepted into the scholarship. Do not make assumptions because the reviewer might look for evidence fo that. By the way, since you are taking English in your school, you have the option to submit an alternative language proficiency certification ( in this case, for English). Look into that if you want to get a better chance of consideration based on language proficiency.
By the way, you dropped 2 language learning possibilities upon your arrival in Korea. You cannot exclude those languages because you mentioned it as part of your pre-arrival program. It must be included in the post arrival language learning path as well.