The faintness of the line has nothing to do with the level of thc metabolites.
Blood tests are only good to detect drugs for 3 or 4 days.
The results come back usually in 3 business days.
Sounds like you'll be fine. Do a little dilluting the morning of the UA.
Drink about 30 ounces of gatorade
pee 3 or 4 times and use your midstream urine.