Brand new unfortunately man. The salt solution rapidly denatures the hormone. The only reason it is added is to mimic the body's saltiness upon injection.
Bac water on the other hand simply just keeps the solution sterile. All you really need is HCG suspended in water - but of course that would breed bacteria without a sterile agent.
Just use 500IU 3 times a week or use 700IU 2 times to use it up. Will be fine for just for one week.
Also: Why 2ml? What they usually give you is also not enough, and is for giant then-and-there doses. Remember HCG is a female fertility hormone. The salt solution and what little they give is for that purpose.
You need to use 5ml (500 units, so you would fill a 100 unit insulin syringe 5 times) per 5000IU, so 1ml becomes 1000IU (100 units). Then you can use your units on an insulin pin to accurately get your dose.
10 units is 100IU, 50 units is 500IU etc.
Usually you buy Bac water in 10ml vials like any other gear, so one Bac water vial is good for two 5,000IU HCG kits. Ideally you'll need a seperate sterile vial to store this in. Otherwise I'm sure you can see where this is going - you'll have to ditch half the 10ml vial down the drain, so the other half still left in the vial can become your HCG solution in THAT same vial. You simply draw a bit out, squirt it into your HCG powder, draw it back out and then squirt that into the Bac water vial and gently swirl it around. DO NOT shake it. Then bingo, mixed sterile HCG.