Am i going to get fired?

I just started my job almost 3 weeks ago, im a cashier/customer service ociate and im not a bad worker im jus still learning as i go. I do what im told, im polite to everyone. I worked a 8 hour shift last night which doesin't bother me at all, and the shift ended at 11 pm last night and I had to be back at work at 7 am well my phone was on silent from the night before and i forgot to turn it on to wake me up in the morning so i woke up 2 hrs late for work! and I never do something like that so I rushed got to work as quickly as i could by then i was 2 1/2 hrs late, I know theres a probation period where they could decide they don't need you or dont think you are right for the job, I really like my job and really would like to keep it. a girl who started with me had already called off 3 times in the first 2 weeks we started cause of illness reasons but didn't bring a doctors note so shes getting fired i just am scared they dont think im punctual and iam! do u think im gonna get fired? I really need this job how can i prove to them im reliable!