It's not wrong, please don't worry about it. You can write notebook with hiragana and katakana. Beginners do the same and in my opinion, it's much better than using wrong kanji. However, I'd like to recommend you to write the English sentences, too, because hiragana and katakana don't have meaning itself and sometimes we don't get the meaning. Besides putting spaces between words would be helpful when you write only with hiragana and katakana to make each words clear although any spaces aren't necessary for Japanese sentences. Ex.) わたし は ジュリア です。(I'm Julia.) Please try and good luck!