Advice Please??

I hope I don't sound stupid with this...
But I have been meaning to quit my job for the past week but I kept putting off because I have built it up to be something really frightening. Now I'm losing sleep wondering how I am going to tell me manager I am not doing anymore shifts... (I have a shift on Sunday too) but I really can't face going back there..

I started uni 3 weeks ago and have more work than I expected and my manager is phoning me every couple of days mithering me about this apprenticeship she forced me to do... and it's stressing me out so much and I don't think I can phone tomorrow because I know she'll have a go at me..

I bet I sound so stupid :(
But any advice guys?

Thanks xx

If you don't need the money from work and uni is the priority then you're better off dropping it if it's causing you extra stress. If you leave properly she can't be angry with you and it doesn't matter if she is as you don't work there anymore.