While I’m not a mechanic, I did do my time as an apprentice... just keep your head down, ask smart questions, don’t fall for the bucket full of spot welds prank like I did!!!, and you’ll be fine. If they do let you go, there is always more work, especially if you’re competent and can show up on time everyday without complaining. I had the same attitude as you when I was 18 and less than a decade later I’m working at my dream job.