Was this a med error?

I am in my first year as an RN and have been off orientation for three months. I feel pretty confident in my skills and don't usually feel hesitant to ask questions from my coworkers; I work with a great staff. Still, I feel very new and unsure of myself at times.

Last week I had a patient two nights in a row. The first night she was getting 2mg Dilaudid IV every 4 hours for pain. When it came time to give her a dose my second night with her, I drew up a full 2mg and diluted it as usual in my 10ml saline. However, the orders had been changed to 1mg every 3 hours. This was also my unit's first week going "live" on our electronic MARs, and while I should have been more cognizant of the 5 rights in the first place, I felt a little frustrated at not having that "one last check" right there on the paper MAR in my hand like we had before. I was already in the patient's room when I brought up her MAR on the computer there to do my last checks when I realized my mistake. I ended up pushing only 5ml of the syringe.

Because it was diluted and dispersed in the saline, did this still equal 1mg? Should I have gone out and redrawn the Dilaudid? Obviously my gut is telling me yes, that would ensure a full 1mg. Was this a major med error I should have addressed?