C.R.I. is cop-speak for "confidential, reliable informant." The police bear the burden of proving the informant is reliable so, for now, let's just call this person a rat.
In a controlled buy, the cops usually search the rat to make sure he isn't carrying any drugs, give him marked bills ("marked" means the serial numbers are recorded, not that there are any actual markings on the money) and observe him while he makes a drug deal. The rat may also be carrying a recording device. When he comes back, he is searched again.
Your post is a little confusing, but it sounds like the rat gave the money to your (so-called) friend, who went back to the rat with drugs he said were purchased from you. That isn't really a controlled buy since your "friend" is the only one who says the deal happened.
There is probably a good issue here for a motion to suppress evidence, but it isn't some do-it-yourself project, like fixing a leaky faucet, that you can do with some advice you got over the Internet.
Because you apparently have the search warrant affidavit, I am assuming you already have a lawyer because these affidavits aren't usually released directly to the defendant. Your attorney should be able to guide you through the process. Posting any more information on a public forum can only hurt your case.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
There is also a motion to disclose the identity of the CRI if you don't already know it. If the CRI has evidence that is relevant to your case generally his identity must be disclosed. The goal of this motion is tricky. You do not really want the CRI to testify as this would make things worse for you. Often, however, the DA does not want to give up the name of the CRI even after the court orders it. In that case the DA is forced to drop the case. Your lawyer will know if such a motion is appropriate in this case.
If your assumption that the cops were not "supervising" or monitoring the control buy is accurate, then you're right, it's not really a control buy. In order to use information from a CRI's to support a finding of probable cause, the cops have to show that the informant's information was reliable and it has to be independently corroborated. Under the facts, as you've described them, the CRI could be making the whole thing up.
Now, I'm willing to bet that the cops were monitoring more of the activity than you suspect. They do not have to be physically next to CRI to monitor the transactions and conversations. Likewise, if the friend confirmed the CRI's version of what went down, then there is probably enough to support a finding of probable cause.