New grad quit?

Hello everyone, I am new to this site.

I am a new grad nurse and I have been working at a post acute rehab center for about 3 months now. I really do not enjoy working here, I was only oriented for 2 weeks and do not feel safe providing care for patient. I get between 10-15 patients in addition to new admissions which I understand is normal at a rehab but everyday is different with so many patients with different diagnoses, I feel like I am not learning. Many days I dread going to work and fear I will be putting patients at risk. The other nurses are nice and try to answer my questions but most of the time they are too busy with their own patients to help or show me how to do something I have never done. I have brought up my concerns to the supervisors and they ... don't seem to really care (management isn't that organized here). They tell me its learning on the job and Im trying my best but scared to harm patients and risk my license. 2 nurses have already quit this month and I feel so bad towards the other nurses who have been kind but I am just so miserable here. I got a job offer at a clinic and I shadowed the nurse there. I really enjoyed it and would like to work there. What should I do? Instead of quitting the rehab, I am hoping to do per diem but when I first interviewed at the rehab, they said they don't let new grads do per diem. If I they don't let me do per diem, should I quit the rehab? I would really appreciate any advice or opinions, thank you!