When a buyer Commits to Buy, a sale has taken place.
Most Sellers are only too happy to Honour a Cancel Order request if one is requested before Unpaid Item Case action begins. After that, it’s too late. Sellers rely on sales, not empty promises of sales.
eBay Customer Service will often ‘forgive’ a buyer’s first Unpaid Item strike if you call and ask. It’s the only mulligan you’re allowed, though.
Make sure you’re logged out of your account before leaving your desktop or device. More than half of my Unpaids or Cancel Orders are a result of minors shopping unattended. This can get your account suspended. Don’t let it happen.