iso reading

This coming Sunday I'm going to be going out with some friends to photograph a site that has literally thousands of daffodils then will be going to a site that has the same amount of Trilliums blooming here in Ontario Canada. I want to get the best shots possible with my Fujifilm Finepix S5200...

I have a Nikon D7100. I have my ISO on auto and sensitivity level to 3200. I normally shoot in aperture priority and program modes. With my Nikon D3100 I was able to adjust the ISO to 100 and it would stay there but with the D7100 I turn the back rotating wheel to 100 but on the meter on top...