Hiya! I've been working at Primark since about July last year. I have one friend who has been down on her till too many times to count. If you're down on your till three times, they'll give you a quick training course and pretty much hope it doesn't happen again. She has just been on her third training course (and has only been there a few months longer than me!). . . So they aren't exactly quick to chuck people out for being bad at the till.
It really doesn't matter to much, have you got many WOWs? What's your relationship like with your supervisors/managers? Are you good at any other aspects of the job? (I'm literally terrible tbh, I got a few WOWs and put loads of effort in up until my last review, but now all I do is hide in the changing rooms or go have a chat with people. I can't fold to save my life, my supervisors all laugh at me when I try and break down cardboard boxes, or I try and take baskets to the front of the store.)
You've already been there longer than ten weeks, your chances are looking pretty good. Hope you keep it!