I posted awhile back about this happening with a vial I got from Strohecker's. One vial was definitely low (4 shots short) and the other was questionably low. I stopped buying from them but who knows, might've just had bad luck since a lot of guys swear by them.
It's definitely possible for a vial to be short, especially if it's being compounded by a smaller lab. It's nothing to lose your ->-bleeped-<- over, though... just talk to your doc on Monday and see what they say.