We British And Our Expressions

So having grew up in Hong Kong - a British Colony - back in the 90s, even though I watched tons of American TV and didn't get the Queen's accent, I acquired a lot of British expressions, and one that I use most often is "not bad".

Habitually I would answer a "How was your day?" with a "Not bad" or "Not bad at all." I mean for me not bad means good and not good means bad logically, so I don't understand how people can mistaken it in any other way. How can not bad means bad?

Anyway, I think my own colloquialism has been in my way. So lately, I've caught myself using the word "Awesome" a lot.