I don't have any info on Utest but most tests are accurate into the high 90%s.

You should stop working out if your test is coming up soon. Ideally you want to stop working out 3 days before your ua. You are burning off fat cells and increasing the amounts of thc metabolites in your urine. Switch to a high fat diet as well. If you are going the dillution route try and practice prior to your ua. When you have your ua, do not give your morning void. Follow the dillution sticky except don't do the aspirin (its outdated now) and sub gatorade for water. Eat red meat, chicken to aid with creatine.