We’ve all done something we later regretted. Stalking is not a crime that is meant to capture singular mistakes. There is no set number of times that makes something a “course of conduct”. What is clear is it must be more than once and should be a series of acts. Could it be two, three, or more times? That will depend on the facts of your case.
Usually, if you do something more than once, then this becomes a question for a judge or jury, to decide whether the number of times you acted that way went from a mistake or two, to a “course of conduct”.