I paid for the aurora theme which cost me $575NZD for a small business owner this was a big hit trying to start. I'm in the exact same boat with not being able to show the discounts on the product items, even when it is included in my theme.

I found that if you use the shopify email app and go to create your own template, then you can use your canva designs. You just need to make sure you've saved them as a png and then upload the image.