English to Japanese translation question!

[Afro di Ziac]

Okay, so I'm writing and speaking to myself in Japanese...and I'm not sure if I'm saying this correctly: "Since I didn't know how to write this word in Kanji, I wrote it in katakana."

Is this correct? 「漢字で書けませんから、かたかなでこの言葉をかきました。」

Also, if I were to write this in the plain form(s), is the following how I would say it?
「漢字で書けなくなかったから、かたかなでこの言葉を書いた。」

[Hyperworm]

The end part would sound more natural as 「この言葉はカタカナで書きました。」, but it's not really wrong as-is, I think.

Your plain form has a mistake.
書けなくなかった → 書けなかった (or, 書けない)

[chikara]

..... "Since I didn't know how to write this word in Kanji, I wrote it in katakana."

Is this correct? 「漢字で書けませんから、かたかなでこの言葉をかきました。」......

I'd interpret the the reason phrase as being "because I can't write kanji", not just the kanji for that word, although that does imply "Since I didn't know how to write this word in Kanji".