your board: Rocker Camber shape that is a hybrid camber combining the best of both worlds with rocker between the feet and traditional camber extending from the inserts to the nose and tail!
That tells me it's not the board!
Now, as far as the length, my friend is way shorter than you (5'7" I think ) and rides a stiff 162 and it' his second year! So, although size matters, I think you are within your size! I'm 6'-2 and one of my favorite boards is a 168! So, though size could be a factor, I don't think that's your main issue.
I would say ICE is your main problem learning! It doesn't help everytime you fall that it really hurts, you become more hesitatnt and bail out to complete your turns, etc.
Not sure what level you're at, but I'd pick a nice spot with snow cover and try and complete your S turns and then linking them. Once you get the confidenece, things will carry over to next level.
Oh... I started on a 168 when 1st got into snowboarding BTW!
So, keep the board and keep at it.
All the best...