Substitution questions

[greendove]

My Quick Fix came but I read another thread in this forum about them finding out it's fake piss

Where is this thread? Could you link it? Chances are, they more than likely had issues because of either temperature, or some other mistake.

I took a home test today and I technically failed it, the line for passing is so faint you have to look at it right under the light to even see it.

That's a fail. The test describes that as a "ghost line", which is pretty much a place in the paper for the chemicals to settle if there is no THC in your system. If you're nervous about substitution, you might want to consider experimenting with dilution, and seeing if that gets you your required results and a passed test.