What snowboard size do I need?

I purchased a Burton clash 2013 151 cm snowboard online and it just came in. It is up to my chin, maybe a cm over my chin (without boots/shoes on). I am just about 5'8" and weigh about 130 lbs. I never snowboarded before, but I skate. Many websites say i need 145-155, so i went with something in between, but i am not sure if it's too big now. I want to mainly do freestyle (after I learned to ride), so the websites say should go with a smaller board such as a 145. I don't want to end up with the board being too big, and a hard time riding, jumping, etc. like last season with skis.

SO is it WORTH returning the board and searching for and buying a new smaller board?

Additional question: Would a size M Burton custom 2014 binding work with a pair of size 8 Burton Moto 2014 boots? (smalll bindings go to size 8 boots, and medium bindings start from size 8, plus the Burton Moto boot has size reduction feature so the outside would be 7) The 151 clash recommends only medium bindings.

SO what do you think? Thanks for the help!