My 2 cents

1. Talk to your manager and tell him/her exactly what you said here and in a polite way. However, DO NOT mention layoff, just emphasie that a. inappropriate work assignment; or b. you need ramp up time and help

2. If your boss didn't take any action after that, try to talk to his boss or HR

3. If still no action, take it easy. If you have better choice, just go for it, otherwise, do whatever you can do in 8 hours a day, and don't worry whether the task can be completed or not.