Don't use the pH stuff unless your pH is really off. The rapid pH swing will just stress him out further, and I have not found any of these things to actually work. I don't know why anyone would recommend a fungus medication for an ammonia problem
, so don't use that either. It may take a while for him to recover from the ammonia. Doing frequent water changes (maybe another one tomorrow, and then every other day) of about 25% should help until you tank finishes cycling. Just don't rinse out the gravel because that is where the benificial bacteria will colonize. If your betta really seems to be having a hard time, you can replace more water during your water changes, just never do 100% because that will start the cycle all over again.
PS: Never trust the people at pet stores. Most of the time they are either trying to sell you something, don't know ANYTHING about fish, or both!