If we’ve understood your question correctly, you would like to know if a 750-W baseboard will meet your heating needs in a bedroom that is 13 ft. x 13 ft.
First, heating needs vary considerably from one home to the next. A room’s heating unit is generally selected based on heat loss in very cold temperatures. These losses depend on factors including the room’s insulation, size, windows and direction.
In addition, even when the right heating unit is installed, the system may not be able to maintain the set temperature in cold snaps. This makes sense since there’s no need to install overly powerful units for just a few hours of very low temperatures. In these instances, using auxiliary heaters can help maintain the set temperature.
However, if the system does not heat your home to a comfortable temperature in normal winter weather, you should contact your landlord or a master electrician to adjust the system as needed.