I’m not sure if we accidentally got a California king but the king size mattress fits width wise but not length wise. There is a 6-8 inch gap at the foot of the bed. We bought this when my newborn was a week old and just kept it out of convience but it is now proving to be super inconvienent. My mattress measures 76” x 80” and there is a big gap. Not sure if it’s too late to return or exchange (a year+ later) but hoping we can figure out a solution!