You still have air in your cooling system most likely. That is the most common cause of low heat in the passenger compartment after a repair on the cooling system. This is the proper fill procedure.
You need to have it on full heat due to the heater control valve on the heater core lines. When not in full heat this valve is closed and will allow air to stay in the heater core. When opened it allows air into the cooling system and will cause low heat. If this procedure does not work then your heater control valve has probably failed