He hasn’t been sentenced yet and if you remember he was given the opportunity to withdraw his plea.
I have no doubt his plea will now be withdrawn, either by him or the Judge will refuse to accept.
Flynn will be free one way or another.
IIRC, the judge was incensed at Flynn, because he was obviously trying to give him some wiggle room for exactly this kind of thing, because it was clear the judge saw he wasn’t guilty of anything, but Flynn I think was beaten down by the process and just wanted to get it over.