I'm pretty sure you'll be fine man. I remember reading somewhere on the internet(so i might be wrong) but it said if you're not a heavy user it should be out of your system 13-25 for someone who hasn't smoked, for a regular user it can take up to 45 days, and I've heard that heavy users can take up to 90 days to test clean. But it also depends on how fast your body metabolizes it and your weight and all that other crap.
But i don't think that an eight between three people will test you positive. Lets say it takes 30 from July 15th to get the THC out of your system, then it SHOULD be out(not positive on this) anywhere between august 14th-20th, since that was about 15 days ago you set the clock back again and you're back at ground zero with what you smoked last night, say that takes about 20-30 days(only because there is so many different things that effect how your body gets rid of THC) then you should be clean somewhere around august 20th- august 30th, so in MY opinion, you're home free.