I rescheduled my Walmart orientation!!! I need advice?

Ok so I got a call from Walmart hiring manager saying that I had orientation Thursday but I told her that I have a very very important doctor's appointment and she said that there is another orientation next week & that she would give me a call this Friday with more details on what time to show up. Normally I never reschedule anything & now... I'm freaking out. What if she doesn't give me a call :( does this messes up my image & job offer :/ will they give my job to someone else. Has anyone been in a similar situation?
I rescheduled my Walmart orientation!!! I need advice?
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