Call them immediately. As nurses, we have a lot of things on our minds, and though sometimes we are required to be superhuman, we are merely just humans, so mistakes are inevitable. With that said, it is very important that you own your mistake, report it to your supervisor, tell he or she the truth, just as you explained, and learn from it. Next time, put it in your pocket or write down on your brain 'WASTE ATIVAN.' I have to do these things because I can be forgetful. You will learn things like this with experience. A lot of nursing is learning the hard way, this may be one of those times. Being scared is normal, they may ask you to pee on a stick, and guess what?! You will pass, because, after all, you did not shoot up the Ativan.