So confused with IUI

Last month my IUI was after I ovulated. Had a positive opk Saturday 8pm, bloodwork on Sunday at 8am showed I already ovulated. IUI was 10:45am Sunday. Well for this IUI I asked for an ultrasound before the IuI to make sure I didn't already ovulate. The nurse said it's not necessary because that's how IUI is done. I was under the impression it was done before ovulation. And she said the IuI was done close enough to ovulation. She kind of made me feel stupid