Drug Test for hospital pre-volunteer

Sorry to add this question to the mix but I am way paranoid and wanted some advice from experts.
I am not an avid pot smoker, I take maybe a hit or two before I fall asleep. I am around my husband who smokes it all the time. I was accepted into a volunteer program at a hospital (which is associated with the nursing program I am starting in fall). They did a random urine drug screening test (for a volunteer position! lame!) and I had smoked (only one hit) the night before. I added clear toilet bowl water and a little sink water to the test, in hopes that it would dilute it to either mask the THC or have it be too diluted to give accurate results and I would need to retake. I took an at home test and diluted it and it came out as a very faint negative, but still a negative (I know, I know lab tests are probably much more accurate).
Anyways - I am freaking out that I am going to blow the test and that they will inform my nursing school. Would this even be legal? for them to inform my school? I already took a urine test for the program and passed (I had quit smoking a month before) and I live in CA, would THC still blow my chances to stay in the program? AND are my chances of being positive very likely?
Thank you for any advice, and please don't give me any speeches on smoking pot and working in healthcare, I only smoke occasionally to help me sleep and I was just enjoying it over summer until I quit for the program.

I think you might have screwed yourself by trying to dilute your urine, especially if it's a hospital administed DT.They usually do a 5 screen test on nursing/EMT students where i live currently. Hell you might just have to take a retest if anything. But worst case scenario is them finding the dilution and/or thc and not being in the volunteer program. I think you could still get into the class though

If you don't have time to get clean, pick up some synthetic urine.