Get yourself a fifth wheel for a pickup. Flat bed or what ever. Cut your teeth on learing to back up one of them. Yet in this job its all about repetition. You will either learn it or need to walk away. Personally I love backing trailers. Tho the trailers that are at the school were attrocious. Aligned for towing, not for backing.
Real talk. You are probably gonna suck for a while until you enough practice in.....we all were there once so it's not an attack on you just the way it is. Just stay calm, don't overthink it and make small movements to get thru what you need to and the rest will come later with experience. If I could give one tip for backing....
The 90 degree alley dock is what is unrealistic. The beauty about the 45 is that you get more space on your blind side. Also, you don't have to turn the wheel that much. The other drivers have said it, but make sure you watch your trailer tandems. They tell you exactly what to do. Don't Jack knife it too much, especially under a heavy load. You don't want to risk tearing up your tires. You want to keep your tires rolling. If they stop moving, you're not doing something right. That's why the 45 degree back is better
Try thinking of it not as backing up, but driving in reverse. Your setup is the most important part, if it’s to far off, pull up and start over. It’s impossible to explain without being there to show you, but ideally, you want your trailer on roughly a 20-25 degree angle towards the spot your backing into, and your tractor on about a 10-15 degree angle from the front of your trailer. The back of your trailer should be between 5-6 feet away from (in front of) whatever is to the left of where you are backing. If you can visualize what I’m saying, you should be able to start by backing with steers straight, and as the trailer turns into the spot, make SLOW adjustments with the steering to follow the trailer into the spot.
I’ve been at this for going on 30 years, and I’m the first to say, there’s no shame in a pull up, but there is in backing into another truck. I’d rather pull up 10 times than tear someone’s mirror off.
I see trucking school as unnecessarily brutal. Pull up three times and suddenly the world is ended. You cannot imagine spots Ive gotten into a thousand pullups or god help me a wriggle even. Add a little wheel watch for the trailer to exhibit the input you just added to wheel. Eventually you will have to get straight. Don't rush it. My stragety is to buy a toy. Hold onto the steer axles of that toy and try to back that between two books on the tabletop. Sooner or later you will realize you are simply driving backwards. Thats what backing is. Remember in the real world Anything is possible in backing. I remember one time I finished a overnight to Mechanicsburg PA from Toledo in a winter storm. I was too tired to function. they gave me 22 docks to pickfrom on what seems to be 4 acres of pavement on front of those docks with nothing in the way. Nothing at all. I could not do it. Because when the body and mind are overtired higher functioning such as backing and the critical calculations pertaining to is impossible. After they finished laughing at me, someone else took care of it in a few moments. Do not get all aggravated in school. You will have all day to be aggravated in the real world.