OP can definitely collect on the Room Type Guarantee provided the line, "guaranteed - king bed," was on his reservation. Let's not forgot there have been problems on Marriott's web site with the bed type in our profiles not carrying over and being guaranteed in our reservations. If this happened to the OP that may be why he was put into a room with two beds.

Hopefully, the OP remembers to invoke the guarantee, if it applies, before check-out.

Regards,

RIP...