you can smoke the day before if you're willing to chug a couple pints of vinegar. But, you can't dilute it any, and you'll likely feel horrible for a few hours...all it does is change your body pH to a point where the test itself is ruined. They'll contact you for a retest in about 6 weeks time if you do.

But, where you are right now, you should be fine. (Unless they ask for some hair too. Then you're probably screwed.)