What province... if it's BC or Quebec sure... go for the 160cm then.
Even Alberta maybe... but if something like Nova Scotia... I've met two racers from the Nova Scotia team ... well ok they were girls
but still, they were not that great riders as I would have expected them to be.
If you ALREADY have it (and didn't pay full price for it... hopefully 50% off right?)... just ride it as I agree that unless you are like 5'4"... you will be gaining some weight the next few years (although I graduated high school 5'9" 125 lbs myself). If you paid full price, then I would definitely return it.
In my opinion... you are getting negativity because most of the people on this forum can't actually carve a snowboard at speed very well ... and so they get really short boards to compensate for their lack of skill. They can't IMAGINE someone being better than them and being able to ride a snowboard 3-6 cm longer... that's crap, but at the same time you need to be realistic about your own abilities. You must have some type of coach/advisor that snowboards, don't you?