You have left the $col_width and % in there, which ought to cause an error and probably have the inline styling ignored. Did you put a 200px width in the stylesheet?

A better way to alter this would be around line 100 in the Column Grid product_listing.php:
PHP Code:
  // Used for Column Layout (Grid Layout) add on module
  
$column 0;    
  if (
PRODUCT_LISTING_LAYOUT_STYLE == 'columns') {
    if (
$num_products_count PRODUCT_LISTING_COLUMNS_PER_ROW || PRODUCT_LISTING_COLUMNS_PER_ROW == ) {
      
$col_width floor(100/$num_products_count) - 0.5;
    } else {
      
$col_width floor(100/PRODUCT_LISTING_COLUMNS_PER_ROW) - 0.5;
    }
  }
  
// Used for Column Layout (Grid Layout) add on module 
Change to
PHP Code:
// Used for Column Layout (Grid Layout) add on module
  
$column 0;    
  if (
PRODUCT_LISTING_LAYOUT_STYLE == 'columns') {
    
//if ($num_products_count < PRODUCT_LISTING_COLUMNS_PER_ROW || PRODUCT_LISTING_COLUMNS_PER_ROW == 0 ) {
      //$col_width = floor(100/$num_products_count) - 0.5;
    //} else {
      
$col_width floor(100/PRODUCT_LISTING_COLUMNS_PER_ROW) - 0.5;
    
//}
  
}
  
// Used for Column Layout (Grid Layout) add on module 
The remaining line
$col_width = floor(100/PRODUCT_LISTING_COLUMNS_PER_ROW) - 0.5;
will automatically make all products width according to the per-row setting, so if you were to change it to 3 per row you would not need to re-edit the code.