1) Perjury trap isn't a legal thing. If somebody sets a "perjury trap" and catches somebody, that person is still guilty of perjury, that's how the law works. That's akin to telling your buddy "I got a ticket for going 100 in a 30, but I'm going to get off because the cop was setting a speed trap".
2) Regarding setting the trap? How did the FBI know Flynn would lie about his contacts with the Russians? When they asked him about his conversation, he lied about it, how did they know he would lie about it? Why did he lie about it?
3) The FBI handwritten notes have one sentence that he did not have the appearance of somebody who is lying, i.e. no stumbling over words, eyes looking up, fidgety, etc. So that is a pretty ginormous extrapolation to take one contemporaneous note from one agent and apply that the entirety of the FBI. They knew he was lying the second he lied, they already knew the answers to the questions. They charged him with lying. He pled guilty to it, under oath to a judge.
Flynn fucking lied, to the FBI. That is a crime in this country. He will not get off. None of the bullshit that has come out changes the fact that he lied to Federal officers. Do the crime, pay the time. Or was Flynn would say/chant "lock him up, lock him up".