Not so!  Taft made an even bigger error. 

As was thoroughly discussed in the blawgosphere in the last 24 hours or so, there is likely no person anywhere with standing to challenge the oath as void, and in any case taking the oath is a condition precedent to executing the office; it is not actually important that it be done a particular way.  It's a formality.  The presidency began at noon, as everyone agrees.  Taft, in administering the oath to Hoover used the word "maintain" instead of another word, I think it was preserve.  There is no non-crazy person who believes that Hoover was therefore not actually President.

I would point you to a Wikipedia essay that might help you relax, but then I'd be in need of similar medicine. HAND.