Story title (5/5) 
I love the title, it's definitely eye catching and beautiful. I will set aside now that it's not your idea. 
In this case I reverse the rule and I say that the story really fits to the title. Oh, and I have to mention the chapter's title too: 'The little boat'. It only makes sense if you read the whole story; I have to say it's beautiful.

Poster and BG (if there is any) (9/10)
Well, the colour of the poster and the background fits to the meaning of the story. The background is a bit strange though, it would be better if the poster and the bg have matching colours. I would prefer if the poster would be a bit sharper, but the birds in the background is a great idea. I love the fonts as well. 

Foreword (8/10)
It doesn't contain anything else but your author's note. Since it's a oneshot, it doesn't really necessary to put anything there, but it looks better, if the story has a proper foreword. Maybe you should put there a little snippet of your story, a quote or a little part from the lyrics of a fitting song, but it doesn't really necessary.

Description (9/10)
The description is almost perfect. There is only a little mistake and I have a question/suggestion too. I think that the last sentence 'Until he disappeared.' is not necessary. I think it tells too much about the story. We don't have to know right at the beginning that he will 'disappear.' 
Mistakes/suggestions:

Original: ...all she knew was the she had to.
Modified: ...all she knew was that she had to.

Original: ...so many years until he came. Until he made her realize.
Modified: ...so many years until he came, until he made her realize.

Plot (14/15)
The plot is beautiful, really well-biult. I loved that you were descriptive, and loved that you separated the story into little paragraphs.
I loved when Joon Myun always asked her in the end of their dates "What ties you to him?". We all knew that someday she will have a different answer, but it worth the time to wait for it. There were little hints throughout the story about Joon Myun's illness, that's good, but in the end Joo Hyun realized that she knew about his illness all along, moreover she has his handkerchief? You should have to point this out earlier in the story, because in the end it looks too sudden that 'Hey so I know him, yeah, and I knew he's going to die, and yes, I have his handkerchief.' 

Character (19/20)
The characters are great, Joo Hyun's character's change is good. There is one character who I didn't really understand; she is none other than Yoona. She didn't hate Joo Hyun, she just envied her, so she only dated Luhan to make Joo Hyun cry. I don't know, just because you envy somebody you don't want to make her cry or maybe this is just me. So yeah, she was a bit confusing.

Grammar/Spelling (15/20)
Despite English is not your first language the grammar is pretty good. There aren't huge mistakes and the story is totally understandable from the beginning till the end. However there are some typos, sometimes you forget to put the period on the end of the dialogues, and sometimes you forgot to put the verbs to past tense.
Now I will list a few words that you should change in this form: you used --> you should use instead
garden planner --> garden designer
hand chief --> handkerchief
sakura --> cherry blossom
sakura tree --> Japanese cherry tree or Cherry tree
sakura flowers --> cherry blossom

I won't point out all of your mistakes, just a few one.

Original: ...that made her burry her head in his should and cry like there was no tomorrow.
Modified: ...that made her bury her head in his shoulder, and cry like there is no tomorrow

Original: ...not minding that his shirt would be later be wet and dirty because of her make up- all he wanted was her to be okay and Joo Hyun couldn't ask for more.
Modified: ...not minding that his shirt would later be wet and dirty because of her makeup....

Original: ....- not only she had meet her arch enemy but no she cried in from of a random person...
Modified: ....- not only she had met her arch enemy but she cried in front of a random person...

Original: ....Pororo shook his head and close his eyes enjoying the week sun.
Modified: ....Pororo shook his head and closed his eyes enjoying the week sun.

Original: ...the mood was ruined as they bumped into Luhan and his mistrees.
Modified: ...their mood was ruined when they bumped into Luhan and his mistress.

Original: ...his face becoming red because of the fear of being find out.
Modified: ...his face became red because of the fear of being caught.

Original: Not even one bit.
Modified: Not even a little bit.

Flow (10/10) 
For me the flow is perfect. Not to slow, not too fast.

Originality (8/10)
There is a cheating boyfriend, a girlfriend who knows everything but don't make a single movement, then comes a stranger and helps the girl to move on. The idea itself is not original, there are a tons of fanfics like this, but the way you wrote this story is a compensation for everything.

Overall Enjoyment (10/10)
I loved it. :D

Ending (of there is any) (5/5)
The ending is great. I'm glad you wrote the last paragraph, because without it, I would fell that the story is not complete. There are a lot of oneshots that end really abruptly, but this is good.
Maybe I would appreciate if you wrote what did she mean about "I've fulfilled my dreams". Did she finished the college/university? Does she have a job, a loving boyfriend? Nothing much only a sentence or two, a little summary, like the part when they get to know about each other's family background.

Bonus (3/5)

Total: 115/130 points

::lexayoo's note::

I so loved this oneshot, I almost cried when she listened to his voice message. You're really a great writer. I hope I could help. Good luck on the contest. ^~^