When I first started the Write It Sections, I had a mediocre understanding of the Hiragana and Katakana. Unfortuantely, this section is a bit clugy for several reasons:
1. You must match up the kana exactly as it is written in the answer key (a.k.a. Not Rated section).
2. You also need to know how to use the virtual keyboard, as there are times when you need the diagraphs and diacritics (e.g. きゃ and ぎゃ).
If I can, I usually leave this part for last or go back and do it over again!
Best suggestion is go through the Lessons that deal with Hiragana one by one, practicing writing out the symbols as outlined in each Writing section. Keep pracicing, over and over again.
Just to give you an idea, I've been writing kana now since May 2013, and I can honestly say that I haven't got it down yet. I have to write it at least 100 times a week just to stay focused and to recognize the kana in each context.
For now, コッド - san states, just continue to go thorugh the charts (or the lessons on Writing) until you are comfortable with the Hirgana and Katakana, then go back and try the Write It Sections.