Featured image rotating on homepage

Hello
I’m using Fashionista and having problems with my featured image.
The image in the post looks fine – but on the home page it is rotating, sometimes shrinking – there is no consistency and I can’t work out how to stop this happening.
The blog is https://www.mysundaebest.com and the post i’m talking about is https://www.mysundaebest.com/2015/07/milkmade-my-day/

Any suggestions helpful – and in layman’s terms please, i’m a newbie : )
THANKS!