Below, you'll see any text that was highlighted with comments from the reviewer.
The odd relationship between the boy and girl is very intriguing and has the reader speculating, which I like a lot!
You did not divulge any of their history which makes the girl's actions more interesting.
All that being said, it is a little bit unclear what the "mistake" is that she mentions. Was the mistake that the boy didn't shoot her before? If so, mistake may be an odd word choice as it suggests that the boy, who seems to be more of the antagonist than the girl, meant to kill her at some point, yet there's no indication that he would have any motive. If I'm just wrong here then disregard that.
The writing itself is very strong and this story absolutely catches the spirit of a flash fiction.
This piece is a bit vague in some areas (what do you mean when you say "he had her right where he wanted her?" why does he want this?)
Also, some of the dialogue is a bit cliche. It's interesting for sure, but I would rephrase some of it to make it a bit more original.
Very fun to read! Loved how you ended it!