I used to smoke a good amount but then stopped for about two months then smoked 1 more time a day ago will i pass a drug test i took niacin and drank water?

Not with your last use being less than 24 hours before the test.

I have to wonder, though: You were off pot for two months. When you know you have a test, you smoke the day before it? Couldn't you have at least waited until AFTER the test?