Any reason why you treated 小さい as a な-adjective?
“小さい”の検索結果（435 件）：英辞郎 on the Web：スペースアルク reveals usage is as an い-adjective. It is sloppy to treat it the way you did. In daily life, it is more proper to treat them as い-adj.
I hesitate to complain about you offering lessons when you make mistakes, but it's a much more minor one than usual. Although it still is difficult for me to stomach lessons that use 私は so much in sample sentences. Japanese people don't use it as much as you have.