<human>: Could you distill the essence of the text into 1-3 sentences?

I'm 17 years old working as a car mechanic at a small shop and just hate my job. I get in at 7 in the morning and pretty much clean the entire time or do whatever odd job they have for me that day. About a month ago I tried putting in my 2 weeks notice because I just couldn't deal with all of the random stuff they make me do instead of what my job title actually is. My attempt to put my 2 weeks in failed when my boss got mad at me and said I had an agreement to work 90 days. I told one of the other mechanics about my attempt and he told me that I'm an at will employee that could quit whenever I wanted without notice. Now after some thinking I'm planning on quitting on the spot to avoid having to face my boss again and have him pretty much punk me into staying. Even though I will quit on the spot I plan on leaving him a letter of resignation to at least give him an explanation for why I left. I just want to know if this is a good route to take and are there any alternatives.
<bot>: I hate my job and tried putting my 2 weeks in but my boss didn't let me so now I'm thinking of quitting without notice but in the nicest way possible.