My form validation isnt working, issue with the JS or html. for uni work

function validatebookclass() {

  var accountname = document.getElementById("username");
  var accountpassword = document.getElementById("password");
  var coursetype = document.getElementById("ctype");
  var numberofattendees = document.getElementById("numb");
  var date = document.getElementById("date");
  var timeselect = document.getElementById("time");
  var ingredientsdelivered = document.getElementById("ingd");
  var dietry = document.getElementById("diet");

  if (accountname.value == "" || accountpassword.value == "" || coursetype.value == "" || numberofattendees.value == "select" ||
    date.value == "" || timeselect.value == "pick" || ingredientsdelivered.value == "" || dietry.value == "") {

    alert("Please fill in all fields");
    return false;
  } else {
    alert("Thank you for booking.");
    true;
  }
}

<form name="bookclass" onsubmit="return validatebookclass()" method="post">

  <h id="ftitle"> Username:</h>
  <input type="text" name="username" size="30" placeholder="Enter username here...">

  <label for="password"> Password:</label>
  <input type="Password" name="password" size="30" placeholder="Enter password here..."><br><br>

  <label for="ctype"> Course Type:</label><br> Introductory
  <input type="radio" name="ctype" value="introct"><br> Amateur <input type="radio" name="ctype" value="amact"><br> Professional <input type="radio" name="ctype" value="proct"><br><br>

  <label for="numb"> Number of attendees:</label> <br>
  <select name="numb">
    <option value="select">Select</option>
    <option value="one">One</option>
    <option value="Two">two</option>
  </select>

  <br><br>

  <label for="date"> Time Slot:</label><br>
  <input type="date" name="date">
  <select name="time">
    <option value="pick">Select</option>
    <option value="10am-1pm">10am-1pm</option>
    <option value="11am-2pm">11am-2pm</option>
    <option value="12pm-3pm">10am-1pm</option>
    <option value="1pm-4pm">11am-2pm</option>
    <option value="2pm-5pm">10am-1pm</option>
  </select>

  <br><br>

  <label for="ingd"> Ingredients delivered:</label><br> Yes
  <input type="radio" name="ingd" value="yes"> No
  <input type="radio" name="ingd" value="no"><br>

  <p id="bclass">If yes, you will be emailed with a further form to fill out.</p>

  <label for="diet">Dietry Restrictions:</label><br> Gluten Free<input type="checkbox" name="diet" value="gf"> Nut-free <input type="checkbox" name="diet" value="nf"> <br> dairy-free
  <input type="checkbox" name="diet" value="df"> Other <input type="checkbox" name="diet" value="other"><br> None <input type="checkbox" name="diet" value="none">

  <br>

  <button type="submit">Submit</button>

</form>