I figure if its getting sent to the lab, they are either doing a GC/MS test or they will test for S/G or Creatine levels
Even though its sent to a lab, an I/A screen is performed first. If the sample registers a negative on the I/A, the test is over as a 'pass' - no GC/MS is performed. The GC/MS is performed only on the drug panel(s) that tested positive on the I/A screen.
Creatinine and S/G is checked as SOP, but this is of no concern unless you have plans of diluting, or if youre planning on using a non-human sample (ie; animal urine, hot water with yellow food coloring, heated Mountain Dew, etc)

Also i would like to add, when i am doing my home test , the negative line for other drugs come within less than 10 seconds, while the THC negative line comes 15-20 second after...is that ... normal?
Yep. No big deal here.