what did I do wrong?

Either of two things could have gone awry...

1. After uploading the picture, you have a limited amount of time to hit the "post" button (I don't know how long). If it takes longer, the images won't show.

If I'm doing a longer post, with images, I usually do all of the typing then go back to upload the photos in the proper place.

2. If you preview an illustrated post too many times, the photos will go wonky. I don't remember exactly what goes wrong with them, but I seem to remember totally wrong pictures showing up in my posts before I learned these two lessons!