<?php
function adjustArray($myArray, $lineLimit = 3){
    $count = count($myArray);

    if ($count % $lineLimit != 0){
        for($i = 0; $i < $lineLimit - $count % $lineLimit; $i++)
            $myArray[] = "";
    }   

    return $myArray;

}
var_dump(adjustArray(array("", "he")));

array(3) {
  [0]=>
  string(0) ""
  [1]=>
  string(2) "he"
  [2]=>
  string(0) ""
}