Hi Mrstep,
In order for your bottom sticky cart to update whenever you add a product to cart, you’ll need to change the code for your theme. Being very honest with you right now, it’s very complicated for me to explain it in detail. But in Dawn theme, there is javascript code that updates the cart number at the top whenever an item is added. In order for your cart number at the bottom to update, you’ll need to include your cart in that existing javascript code or write a different code that will grab the number when it gets updated.
Hope this helps and if you have any questions, feel free to ask here or through my contact email below! 