I actually have a detailed article that shares the common amount of weight you will likely gain during the loading phase, and also tactics for having a little bit of control over that to minimize the loading gains:
For most people on their first round, you will likely gain 1-4 lbs. In some cases you might even lose a little! I did my first round. The article I linked to above shows my loading gains for all 5 of my hCG injection rounds, as well as how fast I lost that weight once on P2 vlcd of the hCG Diet.
I also have an article that discusses how fast you will likely lose the hCG loading weight as well!