I need one help i would like to perform simple validation in jquery but here the problem is that form is getting submitted every time even after giving error message please suggest me

I need one help i would like to perform simple validation in jquery but here the problem is that form is getting submitted every time even after giving error message please suggest me

//// jquery code /////

$(function(){
function checkname(){
var letters = /^[A-Za-z]+$/; 
var name = $("#idname").val();
if(!letters.test(name))
{
alert("only alphabets are allowed");
name.focus();
return false;
}
else
return true;
}

function checkmail(){
var mailformat = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/; 
var email = $("#idmail").val();
if(!mailformat.test(email))

alert("E-mail id is not valid");
email.focus();
return false;
}
else
return true;
}

function checkpwd(){
var pwd = $("#idpwd").val();
if(pwd.length<8)
{
alert("password should be atleast of 8 charachters");
pwd.focus();
return false;
}
else
return true;}

function checkrepwd(pwd){
var repwd = $("#idrepwd").val();
if(repwd!=pwd)
{
alert("password doesn't match");
repwd.focus();
return false;
}
else
return true;}

function checkcontact(){
var contact = $("#idcont").val();
if(contact.length<10)
{
alert("contact no is not valid");
contact.focus();
return false;
}
else
return true;}

function checkcomment(){
var comment = $("#idcomment").val();
if(comment=="")
{
alert("comment can't be blank");
comment.focus();
return false;
}
else

alert('Form Successfully Submitted'); 
return true;}}
$("#RegisterationForm").submit(function(){
if(checkname())

if(checkmail())
{
if(checkpwd())
{
if(checkrepwd($("#idpwd").val()))
{
if(checkcontact())
{
if(checkcomment())
{
return true;
}

}

}

}

}


else{ 
alert("form not submitted");
return false; 

 });
});

////HTML FORM CODING////////
<html>
<head>
<link rel="stylesheet" href="CSS1/stylesheet2.css"/>
<script type = "text/javascript" src = "jquery/jquery-3.2.1.js"></script>
<script src="jquery/validationjq.js"></script>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>REGISTERATION FORM</title>
</head>
<body id="mybody1">
<form id="RegisterationForm" method="post" name="registrationform" action="processdata.php">
<center> <h1>REGISTRATION FORM</h1><table border="2" id="tbl1">
<tr><td>Enter name:</td><td><input type="text"name="txtname" id="idname"></input></td></tr>
<tr><td>Enter Email id</td><td><input type="text" name="txtemail" id="idmail"></input></td></tr>
<tr><td>Enter Password:</td> <td><input type="password" name="txtcls" id="idpwd"></input></td></tr> 
<tr><td>Reenter Password:</td> <td><input type="password" name="txtrepass" id="idrepwd"></input></td></tr>
<tr><td>Enter Contact no:</td> <td><input type="text" name="txtcontact" id="idcont"></input></td></tr>
<tr><td>Enter Comments:</td> <td> <textarea name ="txtcomments" id="idcomment"></textarea></td></tr>
<tr align="center"><td rowspan="2"><input type="submit" value="Register"/></td>
<td rowspan="2"><input type="button" value="cancel"/></td></tr>
</table> </center></form>

</body>
</html>