use sub q for the simple reason that hcg is a water based prepartation, and in the event that your solution has becteria growing in it (likely, ince people like to store it when they arent meant to, its supposed to be used right then and there and the excess thrown away) and you stick it in your muscle, you risk an abscess (bad) or, if it goes into a vein...wow youd be royally fucked
just do sub q. if you get an infection itll be a little pimple. beats the shit out of the two options i described above