To "stare down the barrel of a gun" is to be in a seriously dangerous situation which must be dealt with NOW, before it's too late to respond. It's the sort of thing Martin Gore would write a song about......

The speaker is saying he or she was forced to do whatever they’ve done. Think of a person being held hostage. The hostage is forced to read a statement on the phone with a gun being pointed at their head. This hostage has no desire to read the message, but has no choice. The hostage is telling the message while "staring down the barrel of a gun."

Staring down the barrel of a gun means that someone is pointing a gun at you and is ready to shoot. You are standing looking into the gun's barrel wondering if you are going to die. So this person is saying that they did something, they are not sure what, that has them in a lot of trouble.

It's not altogether clear from the lack of context, but I would say it means that the speaker has been forced to do whatever they've done. A gun has been pointed at the speaker to force him or her.