Just tell your boss that you drank a bunch of water before the test so you'd be able to pee. When I went to quest, they told me to come in with a full bladder. Explain to your boss that you downed a bottle of water on the way to the test and you don't understand how it can be too diluted. Tell them that you're willing to take another test and this time you won't drink so much water. At least you didn't test positive for anything. I think you have a better chance of getting by with diluted pee than a positive test result.