The total price of your trip is based on the occupancy you have selected and depends on the amount of roommates that are in your room.
Each occupancy (single, double, triple, quad) has a different price. The more people you have in your room, the less the total cost of your trip will be.
If your occupancy decreases, it is your responsibility to request another roommate to fill the space OR to pay the occupancy difference.
If your price has changed, review the article Why did my price increase? for more information.