Hello db. Let me try to help :)
You haven't provided a lot of info, but based on what you say, it seems that:
1) you are an intern, not a full-time employee (FTE)
2) Your boss seems to be the one supposedly in charge of the Epicor update, but it also seems that he felt you could be put in charge while he's away. Wait, though: in charge in case the automation he put in place doesn't work.
3) You feel the task it daunting, and you are panicking.
4) It seems you are mostly worrying about the case where the automated update process fails, and people would revert to you to ask for help.
If the above is correct, I'd suggest the following:
1) Use a written form of communication to tell your boss what makes you anxious. Written would help you in case of any legal issue, any wrongful termination, or simply in case your boss will try to blame you for any issue as a result of a failed update.
e.g. "Dear boss, I hope you will have a wonderful holiday next week. I am concerned about the Epicor update scheduled for Monday, Oct 17th, as I have no useful information to be able to support the company in case the update doesn't go as you planned. I just wanted to make sure that you were ok with this, and don't expect me to be able to intervene in case of issues. Of course, I will do my best if something happens, and I would appreciate if you could let me know what's expected of me during the update, or even in preparation for the update (e.g. would you need me to study anything during the weekend?) Thanks."
2) Do not assume that your goal now is to prep for the update, spend the weekend studying Epicor or whatever else. You might still want to do it, but again, it is not required. It seems your boss didn't tell you anything like that.
3) You might want to review your "contract", even if you are an intern and not a FTE. What did you sign when you started working with this company? Try to see if there's anything weird in the liabilities you incur for any wrongdoing. Probably nothing, though. Relax.
4) You're an intern, you're probably young, and this is a great learning opportunity for you. Your anxiety is a consequence of your inability to communicate with your boss properly, even if he might have made a mistake of leaving you alone in all of this. Analyze how the conversation went, and see if you could have done better.
5) Finally, do not listen to the others suggesting that you should polish your resume and run for the hill. It's too rushed. You gave us sparse information, and there's very little to suggest that this would be the best course of action.
Try, instead, to make the best of this situation. And don't panic. Panic is often anxiety, self-inflicted anxiety. You probably didn't do anything wrong; you might have a boss that is not fully aware of what's going on inside your brain, and that happens.
Good luck! Hope that this was helpful in some way.