The chart above reflects the results of the Winthrop University Poll -- done between February 9th and 19th of 443 likely voters in the South Carolina Democratic primary, and has a 4.7 point margin of error.
Biden still has a lead, but it is not a large one. And there is still about 1/5 of voters that have not made up their minds. That's a large enough portion to change the results if they break for one or two candidates.