Dry (unmixed) HCG can be stored in its original unopened ampule at cool room temperature for many months.
HCG that has been reconstituted using the saline solution that came with it should be used immediately. I suggest discarding the saline solution and instead use your own bacteriastatic water.
HCG that has been reconstituted using bacteriastatic water can be stored in the fridge for a few weeks, as long as it is stored in a sterile, sealed container.