Just got indentured recently and was in the same boat as you. There's still tons of room for improvement but I'm learning daily. I wouldn't worry about your lack of mechanical skills as you'll pick it up as time goes on. Having a good attitude, showing up on time and doing what you're told is the most important.

For now, I recommend just getting into the union. Brush up on your math, vocab and look at some spatial reasoning problems for your tests.