How much liquid will cause a dilution?

I took a lab drug test on July 9th. I was testing negative, in the afternoon, on a home drug test, but tested positive the first piss of the day! My test was a 3:30PM and I drank a bunch, bunch, bunch of water (did take Vitamin B to make piss neon yellow)....got call from my employer stating it came back in conclusive, so I could retest. I put it off until July 23....so had 26 days clean and was testing negative on first piss of the day with home drug test. I've felt OK, until now....starting to worry about another dilution result (and I smoked over the weekend)! I took this 2nd lab test at 11:00 AM....I had two cups of coffee and a small cup of water in the waiting room at Health Works. Am I stressing too much about getting a dilution on this 2nd test????? I didn't take any vitamin B and the piss was still a light yellow color. Someone please help me calm my nerves:)!