Yes, in taking care of yourself, your son, your marriage, you are doing the right thing.
Here's the sad truth: You can't change your mother. You can't control her drinking, no matter if you kept an eye on her 24 hours a day. You can't make her stop. Only she can do that. And forgive me for saying so, but it doesn't seem as if she wants to.
Alcoholism is crazy-making behavior. It makes her husband crazy, and it made you crazy for the time that you were staying there. You fall into a pattern of wanting to control their drinking, and you think, "if only they would stop, everything would be fine."
I would encourage you to try an al-anon meeting. The program might not be for you (I'm still making up my mind myself), but I've found some of its messages incredibly useful. You can care for your mother and refuse to enable her drinking.
But in answer to your question, yes, you did the right thing and there is no reason to feel guilty about this, no matter what manipulative tricks she tries. Do NOT put yourself, your son, your family in jeopardy because of her drinking. If she wants to see your son and you want to let her, you might want to consider some restrictions -- as in, their visits are supervised by you and UNDER NO CIRCUMSTANCES is she to drive him anywhere.
Do some thinking about what you will and won't put up with, but don't allow yourself to be guilt-tripped or manipulated. This is a disease, and if she wants to drink, she is going to drink, no matter what you do. However, she will make you crazy in the meantime if you continue to try to control her behavior. All you can do is learn to control your response to it and work on detaching from the situation. We can help you with that here, but we can't do it all. So think about going to an al-anon meeting, or pick up some of the literature -- there's al-anon literature, and there is also some other good literature about dysfunctional families and families of alcoholics.
I'm sorry to hear about your mom, and I know that you are deeply hurt and upset by this. Please take care of yourself and your family at all costs, and keep posting here. We are here to help, and we understand.
Lots of luck to you. Welcome.