If you have not committed to purchasing an item you should be able to delete it from your cart using the "Remove" link.
If you are using the eBay app, try swiping left to delete an item or swipe right to save for later.
If that is not working for you, try another browser.
Using a desktop browser, hover your cursor over the cart icon in the upper right corner of most non-cart eBay pages, then use the trash can icon to delete an item.
