Here is a screen snap of it
Right click on the big image in the center of the screen and you get that  menu.

Fred
If still not good, I will be happy to make a video for you.

The "Please Wait" yellow reminders are generated when Qimage is building thumbs and cache, and you ask it to do a different chore.
Just let it finish the "build" and no more waiting time.
Look above the thumbs and watch the numbers changing.
Fred

After playing a bit - to confirm the image is 100% I will look for four tiny green buttons  on each corner of the print. When it is cropped the buttons go red. So that's a good confirmation for me that I will be getting 100% of my image printed when i get four tiny green button.

Feature request - a much bigger indication/indicator to confirm it is a 100% image - maybe a large nice green box just right under the image or a green colored border whenever it is a 100%. It can get tiring to always have to ensure that the 4 very tiny buttons are green for 100% - especially when it's late at night and one has already done lots of print jobs and there are more to do.

But I can confirm that Fit to Page does not work when you toggle other sizes and come back to Fit to Page. You have to click Auto Cropping Scissors twice to enforce Fit to Page to work as advertised ie. produce a 100% image.