Don't stay in the truck when your partner is backing and don't stand around yapping. Watch their errors. Learn from them. You need every single second of backing practice and knowledge you can get. This is school, after all, so surely you expected to get homework.
Many people try to work a job at the same time they go through school.
This isn't easy. If at all possible, cut down on hours or quit the job. You need your full powers of concentration for school and that's very hard if you're exhausted. Try not to be absent. Most driving schools' biggest enemy is the lack of sufficient time to teach all they would like to.