Anxiety Regarding New Truck Driving Job.?

ok i have an A class licence. that is a tractor trailor. anyway . before i was freaked by backing up. now i am calmer . i have driven smaller trailers for a moving company. i also have a hard time with directions but i have a gps. monday i start with a new company and drive on my own to the usa. from canada.
2 years ago when i tried this with a trainer in the truck i quit when i got home and ended up in the nut house for a time.
this was all due to anxiety . how can i keep this all in check so i dont fail . please help.