Hi,
That's normal. You've set both a fixed price + a percentage price.
So the shipping amount will be calculated as: 35€ + 20% of the total price of the products => 35€ + 0.20 * 428.40 => 35€ + 85.68 => 120.68
It matches your configuration to the exact cent.
You don't want to set the percentage field of your shipping method if you want a fixed shipping fee.
Note that there is no field to configure the taxes since you have the "automatic taxes" setting activated. If you turn it off, you would have to select the tax category used to get the tax rate to be used on the shipping fee.