IUI-trigger shot question

So I am on my third round of IUI (ugh) and I had my follicle scan yesterday. I had a 20 mm, a 13 mm, and a 15 mm. She wanted me to trigger yesterday, but I forgot to order my shot (I’m brilliant I know) and it wasn’t going to come in until today. I had a negative ovulation test yesterday, so she said it was fine to take a trigger shot today. I took a test this morning, and my test was negative. My trigger shot just came in the mail about five minutes ago, and before I took the trigger shot I tested again and my opk was positive. So I did what they told me to take the trigger shot, I’m just wondering if this is a missed opportunity or if this is perfect timing? Aren’t you supposed to take the trigger shot before ovulation to induce ovulation? Since my test is positive, wasn’t I already going to ovulate? These may be dumb questions, sorry in advance.