12 is a very high pH for a buffer isnt it? Perhaps you should say what you are designing it for and what you used to make it before I can tell you. Did you remember to adjust the pH or did you do it wrong?

I have no idea why you have pH 12 because you did not give me enough detail as to what you did. However, if you went over your desired pH. ie., made your buffer too high, you can always adjust it down. Put your buffer with a flea (magnetic stiring rod) on a magnetic stirer and adjust it down with 1M HCL then fine tune with .1 to .01M.