You lie. You die. That's all there is to it.
You are finding out even as we speak that lying to get the job is pointless if lying means that you can't keep the job you got.
The pathetic part for you is that if you had told the truth, you'd have a pretty good chance at keeping the job in exchange for a small risk of not getting the job.
It looks to me that you are only sorry because you got caught. You put yourself in a no-way-out situation. If you don't produce the certificates, you don't get the job. If you produce the certificates and the certificates don't substantiate the claims you made at your interview, you don't get the job. Whether you tell the truth or not, you don't get the job. As Richard III used to say: "what a web do we weave when we practice to deceive" (*)
You did too good a job trapping yourself in your own lies - there's nothing we can do for you. Unless you can claim the experience you gained in your two jobs meets the requirements of the position you are applying for, it's "game over".
(*) Tonyk offers the following correction: the actual quote is "What a tangled web we weave, when first we practice to deceive" and it is from Sir Walter Scott's "Marmion". I would have sworn that Igor-like hunchback Richard III had something to do with that quote :)