A thing I picked up a long time ago, is
If they are off track just move the track to them.
IE if they are trying to follow the story but they end up in the wrong place.
and their is no reason that the one that they are in can't work.
Just use that location and get the story moving along.
Its perfectly ok to change things as long as it makes sense and keeps the story moving along and enhances the fun.
If they spoil something its ok to add a twist on the go.
Your world does not have to be set in stone, the story does not have to be set in stone.
Adapt and overcome.