I don't believe you can remove data using the error correction tool in the software itself, but you can manually edit the data file and remove any info that you want.
You have to find the right file first. In my case it is in the C:\Program Files\Polar\Polar Precision Performance\myname\2006 directory. The file names are in the format yymmdd01 (for the first file created that day, yymmdd02 for the 2nd file of that day, etc). If you open the file with Notepad or Wordpad you can manually edit it.
The last section of the file is marked with a "[HRData]" header. This is the detail list of each reading that was taken. You can delete (or change) any of the lines of this section and it will be reflected in the software next time you view the file. So in your case, you would want to determine when your race ended in this list (maybe by using the heartrate column, which is the first column of data in my case), and then delete everything after that.
I would suggest creating a copy of the file before you try to edit it just in case it doesn't work out like you want.