Polls sometimes are in error,but there have been no polls showing Le Pen having a serious shot at winning the second round.

https://en.wikipedia.org/wiki/Opinion_polling_for_the_French_presidential_election,_2017 

And while one can criticize the Socialists choice, personally i think the centre riight  is the group who really blew it, choosing the right wing thatcher clone Fillion over  Juppe, who would have appealed to centrist and centre left voters.  Fillions victory on the centre right could lead to a Macron Le Pen finale, wth Macrom winning.  Right now Fillion has fallen to 21  percent first round with 20 percent Macron. Talk about grabbing defeat from the jaws of victory. Even Sarkosy might have been a better choice  for the centre-right.