如何在Google电子表格脚本中计算变量，然后返回确认电子邮件

我对此有点新意，所以提前感谢任何帮助！我收到了一封确认电子邮件，其工作原理是基于Google表单提交触发/事件的电子表格 . 但是，我希望能够让脚本从用户的提交中获取两个字段，然后计算要包含在确认电子邮件中的字段 . 一旦我在代码中添加了计算字段（cost1），确认电子邮件就会停止发送 . 我检查了执行记录，它运行得更快，说它执行成功，但没有发送电子邮件......我的代码有问题，还是我要求脚本做得太多？

剧本：

function EmailFormConfirmation() {


  var sheetName = "Form Responses"; 
  var columnNumber = 3;
  var subject = "Summer School Registration Confirmation";
  var gn = 2;
  var sfn = 4;
  var sln = 5; 
  var s1 = 13;
  var s2 = 14;


  var ss = SpreadsheetApp.getActiveSpreadsheet(); 
  var dataSheet = ss.getSheetByName(sheetName);
  var numRows = dataSheet.getLastRow();
  var email = dataSheet.getRange(numRows,columnNumber).getValue();
  var guardianName = dataSheet.getRange(numRows,gn).getValue();
  var studentFirst = dataSheet.getRange(numRows,sfn).getValue();
  var studentLast = dataSheet.getRange(numRows,sln).getValue();
  var session1 = dataSheet.getRange(numRows,s1).getValue();
  var session2 = dataSheet.getRange(numRows,s2).getValue();
  var emailPattern = /^([a-zA-Z0-9])+([\.a-zA-Z0-9_-])*@([a-zA-Z0-9_-])+(\.[a-zA-Z0-9_-]+)+$/; //email reg expression
  var validEmailAddress = emailPattern.test(email); 
  var cost1 = 0
    if(session1 === "Driver's Education Classroom & Behind the Wheel")
    {
      var cost1 = cost1+400
    }
    else
    {
      var cost1 = cost1+180
    }

    if(session2 > 0)
    {
      var cost1 = cost1+180
      return(cost1)
    }
    else
    {
      return(cost1)
    };
  var body = "Dear" + " " + guardianName + "," +
  "\n\nThank you for submitting summer school registration for" + " " + studentFirst + " " + studentLast + "." +
  "\n\nYou have selected the following for Session 1:" + " " + session1 +
  "\n\nYou have selected the following for Session 2:" + " " + session2 +
  "\n\nIf any changes need to be made, please contact the office." +
  "\n\nYour total fees due for summer school are:" + " " + "$" + cost1 +  
  "\n\n\nSummer School Registrar";

  if (validEmailAddress) {

      MailApp.sendEmail(email, subject,body); 
    }

  }