1 weeks notice or flat out quit?

I started working at KFC last week, 2 shifts a week so I've only done 2 days and then I got offered some full time work at a rest home I do casual at.

I mean, this is more like, what do I say? Because 1 weeks notice seems stupid, I'm virtually useless to them because I don't know anything so asking me to come in for my last 2 shifts wouldn't make any sense.

Is it okay for me to just put it in writing that I'm done, thanks for the opportunity blah blah? I've not had to quit a job before, lol.

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