It always pays to call the property directly during the work day when a senior manager is on duty. Websites are fine for routine business travel, but good managers know the situation and may have a room which meets fire code for 4 people, but isn't particularly desireable and will cut you some type of deal.

But, showing up with more people than booked is a poor idea. Either the reservation gets cancelled or you are forced into a larger room and that is at a rack rate far above what you would have to pay even now.