Unfortunately, nobody can give you a definite answer about whether or not a patient will sue. The fact that you know another nurse who made an error with Epi is also not helpful as cases may be settled by the hospital before ever involving RN staff, the RN involved may not be allowed to discuss a closed claim they were involved in, or the patient may have never filed a malpractice claim.
Many more errors are made than lawsuits filed, and the magnitude of an error is not the single deciding factor in a patient's behavior. Attitude of the healthcare team is at least as important as any error that occured. Patients are much more likely to bring suits against healthcare providers they dislike, when they feel communication is poor, or they feel like healthcare providers are hiding something from them. Many patients report they sue less for their own financial benefit, instead they want to get answers or to prevent similar errors from happening to others. These are some of the reasons many facilities will now openly admit errors to patients, and offer a sincere apology soon after the error is recognized. It sounds like this didn't happen in your case, and obviously this cannot be changed.
There are different types of malpractice claims, but generally the patient must show that some harm occurred to them because of the malpractice. In this person's case it sounds like they experienced temporary symptoms, and possibly a longer than normal hospital course for their disease process. While in the grand scheme of things, these are relatively modest, temporary harms, the patient can also claim damages for loss of work, "pain and suffering," or any other conceivably related losses. Realistically, you have relatively shallow pockets, and patient's will often choose to sue a hospital or health system in addition to just the individual provider.
The bottom line is you can't change this patient's behavior any more, but you probably need to develop some better strategies for protecting yourself in the future. If you are this worried about this event, you are probably so distracted you're going to make another error.
Consider your own personal malpractice insurance going forward. Your employer's coverage serves them, not you.