Drug Test Confusion

Hi everybody. Question. Since November I've been a chronic but light smoker. Just a few hits a few times a week. Couldn't even finish a joint by myself. And I would go periods of time without smoking at all. I'm an active, very slender 26 year old female. I have a healthy, low calorie diet, I get plenty of rest and I don't drink alcohol.

As of tomorrow it'll have been three weeks since I've smoked. I drink a lot of water and I take a lot of vitamins and fiber and I exercise. I have taken the same brand of drug test three times. The first time I took it was the day I quit smoking just to make sure it was an accurate test and I failed it of course so that was good. The second time I took it, it was a little over a week ago (about 12 days after I'd last smoked) and I passed. I hadn't really done anything unique that day or the day before (not a ton of water or tricks or anything). Now it's been 20 days since I've smoked and I took a test today and failed. Granted, today I was very dehydrated. Literally no water or fluids of any kind for like 24 hours (I was busy and just didn't think about it). And I used my second urine of the day and it was very dark (almost orange). At the earliest my actual test will be this Friday (so 4 more days and 24 days since I've last smoked but I may be able to make it later). If I go back to drinking lots of water this week and use a later urine of the day, should I be alright?

I'm not substituting so please don't suggest it. I passed a test over a week ago, I feel like there's no reason I shouldn't be able to pass again.