Problems with my part time jobWatch
If you arent happy working there id look for another job. It should be easier to get another job as you already have one.
A trouble with working for small places is often yr wages are paid right out the bosses pocket as they own it, so they tend to get a bit misery. Considering it's indy fast food retail, they need speed and as you say, you're slow and learn slowly, I can empathize with you trying but I can see how that just won't be good enough for them, chippies tend to have high temp staff turnover, it's a pretty crap job. To be honest it DOES sound like yr boss now has it in for you as it's just not working out (tbh see the thing with the 2 folk not getting meals, aye you didn't cause the error, but an attentive server should have noticed this, people waiting for their food and people not waiting for food tend look very different.)
The group of 8 thing- really you should have taken the initiative to ask if the other two were waiting on any food as you should be checking that everyone has what they require but that can't be changed now.
Your friend has been working there much longer which is why she probably didn't get any blame.
Doesn't sound like it's really the right job for you
However you should ask for money you're not paid, that's not ok.
And no harm looking for another job, you might find something you're better suited to or a more caring manager.
You're learning and you'll get better as time goes on. If you want to leave, leave. You have some experience working in the food industry so getting another job should be easier than your first. Things like using your initiative a bit more (double checking if the two people without food had ordered any etc) are all part of the experience, don't stress.