The chances are that all they will check (if they do at all) is that you attended universtiy and have a degree. Did you only put it on your CV, or did you also have to put it on an application form? The difference being that there is usually a statement that you sign on a application form to confirm that you are telling the truth, however, on a CV you don't, so while technically dishonest, it is expected that CVs are embellished from time to time - that is why people are often told that you must fill in an application form and it is not enough to send in a CV.
I agree that you should sit tight and be honest if and when required. Did you pass a long time ago? If so, you might be forgiven for having "forgotten" exactly what degree you have. Pesonally, I have no idea of any of my grades for any exams I have sat. I therefore just put a pass in my CV rather than risk getting it wrong.
Also, if they were really that interested, they would have required you to bring your certificates with you.