Welcome to 4-ch, I hope you enjoy your stay! よろしく!

Let me say that I think your English is very good for a high-school graduate.

I would like to correct your sentences for you, and I hope you can understand my explanations:

>>Hi, loving everyone!^^ I'm 19years old, a Japanese Otaku.

'loving' is not correct here, you can just say 'Hi everyone!' Remember to put spaces between numbers and words, 'I'm 19 years old'

>>I'm a high school graduate who is preparing for another chance to enter a college.(This is called "Rounin" in Japan, a masterless Samurai is also called "Rounin".)

This is very good. Almost perfect! ヽ(´ー｀)ノ
You can just say 'another chance to enter college,' rather than 'a college.'

>>I made every effort to enter college, but college refused me, because I couldn't read/write English well.

Again, this is very good, but here you should say 'to enter college, but the college refused me,' as you are speaking about a particular college.

>>So, I want you to speak to me easily, and point out my wrong.

For this, I would say 'So, I want you to speak simply to me, and point out my mistakes.'
(Wrong is usually an adjective, mistake is a noun).

>>You can ask me everything! I'm not a grim person.^^ I love you all.(^ε^)

We love you too! Here, I would use the word 'anything' rather than 'everything,' - because everything would mean we should ask you all the questions there are!

>>Do you think this sentences childish?

You should use 'these' here, instead of 'this' because 'sentences' is plural. I would say 'Do you think these sentences are childish?' - And my answer is no, they are very good, they just need a little more work!

>>...oh,excursus.
>>I like WWE,progressive rock. thanks for reading

I don't know what you mean by 'excursus' - do you mean 'excuse me (for forgetting these things...)'? Remember to add spaces..
'I like WWE, and progressive rock. Thanks for reading.'

Hope this helps - and I hope that you can one day correct my Japanese!
ありがとうございました!