The navigation has two modes – Following mode for routes designed by your dispatcher and normal navigation to the beginning of planned route, to a depot, etc.
If you are following the planned route and it is not fit to your vehicle, please report it to your dispatcher.
The normal navigation uses proffessional routing which takes your vehicle dimensions and properties into account.
To achieve proper routing, these have to be set up correctly.
You should either set them on first navigation start or later via navigation settings.
For more information check Set Up Truck Attributes section.