Need help please!

Ok so this I a bit off topic (and a little long) from what we normally see on here but it is causing me incredible turmoil inside!!! I got hired for a new job in September for a separate company working in the local ER but I'm not hired by the hospital. I am currently a full time nursing student, a full time mom to a 3 year old boy, and married (I am 23). Anyways I have gone through half of the training and after this past weekend of working almost 20 hours straight I came to the realization that I cannot physically do it all. I have never quit anything in my entire life and always hold mysel to a high standard. Tonight I sent in my resignation letter because my main priorities are my son #1 and being there for him and successfully finishing nursing school!! I still feel like such a piece of crap and hate knowing I gave up so easily!! I know my priorities are in the right place and I sent a letter of resignation and gratitude, but I still wonder Did I make the right decision??