Google-sheets – Else statement is executing when TRUE

I am completely new to coding. I am a teacher and trying to design a lesson planner tool using Google Sheets Scripts. The idea is to have a template sheet for the lesson that will copy into a new tab. That part is working fine. However, to delete the lesson I want to make it impossible for someone to accidentally delete the template. It is succeeding in not deleting the template tab if "Delete Lesson" is clicked.

However, it is displaying the alert that you cannot delete the template for the other tabs (but then deleting the tab as it should) This is the document.

Any help is greatly appreciated!

I used this code at first:

function DeleteTab1() {  
  var spreadsheet = SpreadsheetApp.getActive();
    var sheet = spreadsheet.getActiveSheet();
    var sheetname = sheet.getName();


  if(sheetname != "Template")  { 
    spreadsheet.deleteActiveSheet();

  }

  else {
      SpreadsheetApp.getUi().alert('The template cannot be deleted');
     } 
}

Then I tried this and had the same problem:

function DeleteTab1() {

  var spreadsheet = SpreadsheetApp.getActive();
    var sheet = spreadsheet.getActiveSheet();
    var sheetname = sheet.getName();


  if(sheetname != "Template")  { 
    spreadsheet.deleteActiveSheet();

  }

  if(sheetname = "Template") {
      SpreadsheetApp.getUi().alert('The template cannot be deleted');
     }

}