what do i do if i'm terrified of my boss?

i'm currently employed at my first job part time but it feels more like a forced labour camp. i said i'd work 20 hours a week max, but last week i worked 30 and a half hours. my boss is verbally abusive and i don't know how much more i can take. for example, he tells me the product i make "looks like ****" and that if i better fix it "or there's the door". he tells me to "stop daydreaming or you'll be doing it at home" while i'm doing dishes. and just the other day he approached me without proof and accused me of yelling at my supervisor in front of customers and taking orders without making them, then told me i was on probation and said he'd fire me on the spot if i didn't change by sunday. i don't usually cry but yesterday after work it was the whole walk home.

what can i do? it took me 6 months to get this job and i'm going to lose it after 3 weeks without justification? i have some dirt on their business practices, if i get fired should i make them known? i have to go back in an hour and i'm praying he won't come in tonight.