Help with snowboard sizing?

I doubt this snowboard will be too big for you. 4 cm may sound like a lot, but really it's less than 2 inches difference. Although there are calculators that will tell you your "ideal" snowboard size, the reality is that for every rider, there is a range of sizes that are ideal for various snowboarding activities. For your first snowboard, the recommendation is that it stands up somewhere between your nose and chin. As you progress, you may find that you want something longer for big-mountain bombing or something shorter for jibbing. But I think the board length that you ended up with will be a good starting point, and K2 is a good make, so good luck!