Hello, @antonia,
Please copy and paste the below given CSS code to XStore >> Theme Settings >> Theme Custom CSS >> Global Custom CSS.
.et_b_header-menu .menu li#menu-item-10395 .menu-static-block {
left: 0 !important;
}
The above code will shift your dropdown Menu left to middle and then you have to set the Mega Menu Container width from Appearance >> Menu by clicking on Mega Menu Item: https://postimg.cc/34pV38MT and make sure that your dropdown menu container width must be the same as your Menu has like: https://postimg.cc/DJVpj9SY
Regards 8Themes Team.