No, you don't understand. Scripture is the ultimate authority. If Scripture says 1 + 1 = 3 and Calvinism says 1 + 1 = 2 then Scripture is correct. Reformed theology is a systematic organization of scripture according to fallible men; thus it is not infallible.
Scripture does not mention Calvinism or Arminianism or NFL football. In cases like these one goes to the fallible source of these and other concepts to determine what they contain.
Similarly, you and I are fallible; yet we give our opinion of what Scripture means.
You and I are the authority upon our beliefs of what the Bible says. The Bible does not say what you and I will believe. You and I are the ones to ask when trying to determine what you and I think, not the Bible. Now, if you or I may think the the Bible says "X", one can say we are mistaken and use the Bible as evidence or our error. But in the end one must go to you or I to determine what you or I believe the Bible says.
Westminster Confession: The Supreme Judge, by which all controversies of religion are to be determined, and all decrees of councils, opinions of ancient writers, doctrines of men, and private spirits, are to be examined, and in whose sentence we are to rest,
can be no other but the Holy Spirit speaking in the Scripture.a
a.
Mat 22:29,
31;
Eph 2:20 with
Acts 28:25.