Terrified of Being Fired

I just started my second CNA job after being badly trained and let go at my first job. I am at a real nice facility and everyone is nice, but I find myself constantly asking questions and needing help and yesterday, on my second day, I accidentally clocked out two minutes early because the Nurse told me to go ahead and I was too tired to remember to wait until the official end of my shift.

Now, the Human Resources Manager told me that they are patient and work with new CNAs and help train them and she said during my interview that the sort of thing like punching out a minute early is let go with a small reminder, but I'm worried.

Will they let me go since it appears that I am not getting it after only two days? I am terrified of losing this job since I don't know if a place will hire a part time student who was fired twice and I feel I need CNA experience to become a COTA. I come in to work on Friday and I resolve to do much better that day, but will that be enough? I think I can get changing the diaper of someone sitting on the toilet down then if nothing else.