To state the obvious, if a test is perfect, 2 out of every 100 women told they have a 98% chance of being fine will not be fine, as will 4 out of every 100 women told they have a 96% chance. I think there's a name for the cognitive bias we all have that makes us tend to feel, emotionally, as though a very high chance is the same as certainty, but I've forgotten what it is.
As my nn indicates it was a very long time ago but something very similar happened to me. I've forgotten some of the details and the tests available then were different anyway, but I was given the same 1 in 25 chance of Down Syndrome based on a test I'd specifically said I didn't want. [ETA but without the "next steps" complication - I was given the result, and then I had to point out I'd said I didn't want it.] In my case I hadn't wanted it because earlier in pregnancy I had had, privately, a more reliable test which had given me a low chance, so I didn't want to be confused by data from a less reliable test which I didn't feel I should weight anyway. (I think the earlier one had made use of ultrasound measurements, done when I'd had an ultrasound privately because I'd had spotting and was about to travel - but I forget.)
In my case the next step would have been amniocentesis, and the fact that that carried a risk to the baby, plus that I had reason to think the 1 in 25 was less reliable than the number I already had, led to me deciding not to have it. As it turned out my baby was fine. I understand the difficulty though. It's very individual because it's fact sensitive - it relates both to all the other information you have and how this 1 in 25 contributes to it, and to what you'd do in various situations where you had more data. All the people saying "you obviously don't mind if the baby has Down Syndrome so what's the problem" - pah. Personally I would have aborted for certain DS, but I also knew there was a chance my baby would have DS or some other serious problem and I wouldn't know until abortion wasn't an option. Having a child involves letting your heart go walking around outside your body, as they say, whatever choices we make, but that makes those choices carry more weight not less.
I think if the midwife telling me had really understood why I had not consented to the test, it would have been better if she simply hadn't told me that the test had been accidentally done - but I can see why that wasn't an option for her. They need to have rules about what to do in such cases and it's not hard to construct stories in which not telling would be a terrible thing to do.
Sympathy.