Cordelia,
Maybe you are thinking something else about 12.5? What we mean is the block needs to measure 12.5 unfinished and when it is put into the quilt it will be 12 inches finished. Are yours measuring 12.5 unfinished?
Hope this helps????
I have tired calling you so we can talk this out but no answer. Give me a call tomorrow evening if this hint does not work. Do not get discouraged okay???