I have wrapped the pw.TableHelper.fromTextArray with a Container and set the margin attribute of the container to negative number.

pw.Container(
      margin: pw.EdgeInsets.symmetric(horizontal: -45),
      child: pw.TableHelper.fromTextArray(
        border: null,
        ...),
 ),

what jarinox suggester in the comment will work if need to set margin for all the page, hence, all widgets in it will be impacted. in my case I wanted only the table to be stretched.