You would have been given micrograms of Fentanyl. Certainly not a milligram, and certainly not 2mg, which will probably kill you. For comparison, you require more than 10 times as much Heroin to do that.

This illustrates it pretty well; a lethal dose of Heroin (left) and Fentanyl (right): https://www.statnews.com/wp-content/uploads/2016/09/Heroin-F...

This is why it's been in the news and why you've read about how strong and dangerous it is. Usage in a medical setting is much safer because they have a known purity and precise dispensing and dosage schemes; something you won't find and can't achieve on the street.