I have a K2 snowboard which seems to be in a mild "U" shape - the middle
touches the ground but the area under my feet do not. I can spin in a
circle without having to move down the mountain at all.

Does this indicate a board which is too stiff for my weight (125lbs and
149cm board) or did it get warped from storing it over the Summertime? Is
there anything I can do to it or SHOULD it be that way?