Think this could be a matter of the wrong amount next to each item (the $2 for new users may be for existing users) but it's what the website shows.
Cashback is not qualified for:
* Cashback is NOT applicable for orders made via the UberEats app
* Promo codes or voucher codes not approved by ShopBack
* Returns, exchanges & cancellations
* Gift card purchases unless otherwise stated
Since it's an automatic system it might not be honoured.