THere are 3 basic non-DOT cutoff levels used for THC. 100ng/ml, 50ng/ml(the most common), and 20ng/ml. As this will be a pre-employment test, I urge you to concider substituting a clean sample. Substituting is easy and 100% effective. Free clean urine can be from ANY clean doner. Age or sex of the doner does not matter. Human urine should be used within 8 hours at room/body temp, but can be stored frozen for up to 1 year. To thaw and warm, use warm water. If a source of free pee isn't available, there are dozens of urine vendors on the web, both human and synthetic. Synthetic urine is easier to store and works just as well as human.
I hate guessing on the 'how close am I' question. Get a home test and test yourself. You may already be nearing the 50ng/ml cutoff level. But if you are seriously concerned about the test using the 20ng/ml cutoff, again, substitution is your best bet. Read both the substitution and dilution guidelines linked to in my signature under this post and then decide what is best. Post any more questions and hope that helps. N2