just make some hk friends

there's plenty in Richmond / Vancouver lol. If you have a basic understanding of Mandarin then watching some TV series / drama would help.
I'm whitewashed ish. I can speak fluent Cantonese (much like you, can hold a good convo, but can't pass as honger), but not mandarin, i can't read or write Chinese except for my name and maybe read 60% of the Chinese menu.
What i do is usually watch tv/ movies / music videos with subs and learn form there.
Luckily i have some Chinese friends. It helps ALOT! i think most important is to get out there and actually use the language much like what Shun and Evox are saying, make friends or somehow use the language. That is the only way to learn it. To immerse yourself in it.