Writing Cantonese is difficult not just for foreign learners but also for native speakers, because we have been taught to write standard Chinese, i.e. Mandarin, instead. There are many words that we don't even know how to write. Many Cantonese words did exist in ancient times but are now unknown to ordinary people. Basically nowadays we write Cantonese only in very informal situations, e.g. texting among friends. So, what do people do when they don't know how to write those words? They either create new characters or use characters that have the same or similar pronunciation. This results in a lot of inconsistency. For example, there are three ways to write "bei2" (give), namely 畀, 俾 and 比. 畀 is correct because it was used in ancient times, but it is less common than 俾, which is incorrect but pronounced the same. And those who don't know either of these two characters would write 比, which is simpler and has the same pronounciation. Therefore, natives speakers are very tolerant of such mistakes. We, except pedants, seldom criticise others for writing "incorrect" Canonese words. In fact, it is very common for native Cantonese speakers to mix Cantonese, Mandarin, English, abreviations and emojis in a single text message. So long as you can put yourself across, it's fine.