Legal Question in Criminal Law in California

It's probably (but there are several factors) too late to undo the deal, but the bigger hurdle is trying to get anyone to believe them.

This type of deal usually requires the defendant to testify truthfully. If you recant, you will be saying you testified falsely -- and thus that you breached the agreement. The prosecutor could probably ask the court to re-sentence you, and perhaps even to vacate your plea and put the case back on track for trial. If your testimony was crucial to the case against your co-defendant, the judge would likely grant such a request. There may be reasons why the prosecutor would decide not to do that, but the decision would likely be up to her.

It's also possible that your agreement says what will happen to you if it turns out you testified falsely. If so, the prosecutor could ask the judge to enforce that portion of the agreement instead of throwing it out altogether.

Sorry about your predicament. I will be honest with you, in my professional opinion, I have not seen much success in recanting the testimony.