Reporting by CBS News' Clare Hymes and Kathryn Watson

The gag order imposed on longtime Trump confidante Roger Stone was tightened during a court hearing Thursday, a consequence of an image posted to Stone's Instagram account Monday depicting Judge Amy Berman Jackson with a symbol that resembled crosshairs behind her head.

"From this moment on," Jackson said Stone cannot speak about the investigation, or participants in the case, either on social media or with reporters. He also can't have statements made on his behalf to urge people to donate to his legal defense fund. Stone has pleaded not guilty to seven counts, including misleading federal investigators and witness tampering.

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"Today I gave you a second chance, but this is not baseball, there will not be a third chance," Jackson told Stone, adding that if he doesn't follow the order she will change his "environment."

Jackson said she did find the post made it clear Stone's actions pose a risk to the community, and said the jury pool would be tainted if he keeps going to on social media "fanning the flames."

Stone apologized profusely for the image in court Thursday, citing a "lapse in judgement" and sheer "stupidity" on his part.

"I am kicking myself over my own stupidity," Stone testified.

Stone told Jackson Thursday he was "heartfully sorry" for the Instagram post. The longtime Trump adviser testified in court Thursday that there was no justification for his actions, citing "extreme stress" of his situation. Stone said he's watched cable news and feared what pundits say could happen to him in prison.

"I've been treated for emotional stress," Stone testified, noting his consulting work has been virtually non-existent since his criminal case began.

"I can only beseech you to give me a second chance. Forgive me the trespass," Stone urged the judge.

But Jackson wasn't satisfied, questioning how Stone couldn't recognize the symbol and pointing out that he contradicted himself in his own statements.

Stone's lawyers on Monday night apologized for the post, which Stone had removed shortly after it was posted Monday afternoon. Stone told CBS News in a text message Monday that someone who worked for him posted the image and that it wasn't intended to be threatening.

"I have objected to the manner in which my case was assigned to a specific judge rather than the judge being selected randomly," Stone told CBS News Monday. "The judge rejected the motion by my attorneys from which there is no appeal. I do not believe that I have violated any order of the court and that these sentiments for within my first amendment rights. Any inference that this in someway threatens the judge is false. Because it is open to misinterpretation I'm going to take it down."

Mr. Trump told reporters earlier this month he hasn't thought about a potential pardon for Stone.