Shopify is not far behind Amazon (the e-com business). It's network sees as many unique visitors as Amazon, though I imagine Amazon has more sessions per visitor, but the GMV across Shopify is just shy of half of Amazon. It's still in the same ball park.
What metic are you using? Shopify takes an average of ~$1bn at checkout daily while Amazon is over 2bn.
Yes, Shopify GMV is roughly half of Amazon.