simpleviewer gallery question (only thumbnails are showing)

Hoping someone can help me! I downloaded and installed simpleviewer, but all that’s displaying are the thumbnails. I want a large image with the thumbnails displayed either beneath, or to the left of the large image. I have tried changing the gallery width and height to 100% after reading other posts in the forum, but that did nothing. Also, once I get the main image that thumbnails to show in the proper layout, is there any way to make the thumbnails smaller?

Here’s a link

https://www.megandowntherabbithole.com/pigments/

Thanks in advance!