There is a difference between a room type and a room rate. A room type represents a physical room. A rate represents a certain type of price for that room. For example, a “double room” (the room type) could be sold for $50 (rate A), but it could also be sold for $75 (rate B).
Please make sure that the different offerings of the same physical room are set up as “rates” in the booking channel, not as different room types. Otherwise the channel will believe that you have more rooms than you actually have – which can result in overbookings.
To avoid that, please register rates instead of room types in such cases.