Narcotic count

Have a question for my seasoned travel/ agency nurses. I'm an agency nurse, the other day I was at my assigned facility. At 11pm when the overnight nurse came in we were in the middle of doing the narc count while he stated the number your telling me doesn't match what's on the card it was over by one pill. After reviewing I realized the patient had a 10pm pill that I had signed but forgotten to pop. So he popped into the med cup I administered the pill to the patient and we finished the count with no issues. The next day around 10am I get a call from the DON stating at 7am when they were doing count the pills were off by one pill and that the other nurse stated it was because of the pill I gave last minute during count after he brought to my attention that the pills were over by one. The DON then called my agency stating she had to do an investigation and she didn't want me working during that duration of time for them or their sister companies. This is the first time this has happened ever since I became a nurse. I wrote my statement. I also asked the DON if it was my mistake that caused the 7am count to be wrong why didn't the oncoming nurse bring it to my attention at 11pm? Why did we both sign the book acknowledging the count is right? Any advice on this. I have no interest or desire to jeopardize my license over one oxycodone.