Art Collaboration Rules #1

⇨まずは申込書にご記入ください。This is more natural. we never say お書き込み even kind of polite expression.

2) Please submit completed works to ####@mail.com
[completed works完了した作品（depends on what kind of art)]は####@mail.comに送ってください。(/出す？)

⇨メールを「送る」で正解です

3) The deadline for submissions is March 26th.
締切日は3月26日です。

4) Please inform us at ###@mail.com to request a time extension.
延長が必要だったら上（記）のメールアドレスに教えてください。

⇨上記 is more professional word. 上is also okay but a little little bit childish for me. 

5) Only submit things that you have drawn yourself.
自分で書いたものだけ提出してください。

Actually it depends on the products, if it's written one, 書く is correct. It is picture, 描く。it's like a design using PC, つくる。 Which one does it like?

Is this art event? That's wonderful. I fixed some words for business term. 

If you have a question, i am willing to help you.

Art Collaboration Rules

5) Only submit things that you have drawn yourself.

自分で描いた書いた作品のみをワークスだけ提出してください。

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Hello, Justin. 

Your attempt was pretty good.  I think you can use your sentences as they are, and everybody can understand what you meant.  I just changed the green parts with more common phrases which I see often in statements for rules.

*送ってください is perfectly fine there.  Another ways to say "submit "in this case are メールしてください　or 提出（ていしゅつ）してください。 

*描（か）く＝draw,  書く=write.    They are often mixed-up and kind of confusing, because both Kanji sound  "kaku" and has similar meaning.  But for painting and drawing, 描く is the right one. (-;