If you are staying at the serai, don't place took much hopes on your advanced booking. Unfortunately it is easily "misplaced" etc etc.
This is particularly so during Gurpurabs and major events - where people with connections (politicians etc) are given priority over the Sangat.
Try Sri Guru Gobind Singh Ji Niwas and if somehow you do not get any rooms, there is one hotel directly opposite and another nearby.
Personally I prefer Le Golden Hotel as it is very near to the Clock Tower. It belongs to a Gursikh and advanced booking can be done. Also, if you have hotel booking, your vehicle is allowed to travel right up to the hotel (Roads nearby are closed during peak hours and you have to WALK with your luggage if you get there during those hours or transfer to a rickshaw - Policemen on duty actually called the hotel to ask if there is a booking under my name).
Carry your passport with you at all times.