Hello,
1) We can’t reproduce the issue https://gyazo.com/9f1d12dc45b83419a20498dead34da13 Maybe you make a few clicks one by one at one product and that’s why you get 2 and more item in cart?
2) By default cart widget in header displays 3 items, all the other items you can check by clicking at the View Cart button. If you want to change this limit you can copy etheme_cart_items (blanco/code/woo.php) function into child theme functions.php and change the limit.
Regards