PHP and Javascript/HTML5 Collaboration [closed]

I've recently been working on a fairly complicated game. I've stored information with local storage, but that allows the player to edit it, and does not transfer from computer to computer. The two scripts run on a single server, and I use the following to ping the php server:

function initiateLoginSequence() {
    var isnewplayer=prompt("Hello! Are you new?(Y/N)");
    if(isnewplayer.equalsIgnoreCase("N")) {
        var username = prompt("Enter username.");
        var password = prompt("Enter Password.");
        //parsing code goes here later.
    } else {
        var username = prompt("Enter a username. This will be used for future logins.");
        var password = prompt("Enter a password. This will be used for future logins.","*");
        var req = new XMLHttpRequest();  
        req.open('POST', 'http://69.144.34.106/Scores.php', true);   
        req.send("returning=false"+"&name="+username+"&pw="+password+"&level="+lvl+"&save=true");
        req.send();
    }
}

I then process the results with this:

<?php
   $returning=_POST["returning"];
   $save=_POST["save"]
   $password=_POST["pw"];
   $username=_POST["name"];
   $score=_POST["lvl"];
   $connection=mysql_connect("localhost:3306","****","*****");
   if($returning=="false" && $save=="true") {
     mysql_select_db("userdata",$connection);
     $sqlcmd = "CREATE TABLE ".$username."(
     Username varchar(".$username.")
     Password varchar(".$password.")
     Score varchar(".$score.")
     )";
     mysql_query($sqlcmd);
   } else if($save==false) {
     $sqlcmd="SELECT * FROM userdata"
     $result = mysql_query($sqlcmd);
     while($row=mysql_fetch_array($result)) {
        if($row['Username']==$username && $row['Password']) {
            echo row['Score'];
        }
     }
   } else if($save==true) {
     $sqlcmd="SELECT * FROM userdata"
     $result = mysql_query($sqlcmd);
     while($row=mysql_fetch_array($result)) {
        row['Username']=$username
        row['Password']=$Password
        row['Score']=$Score
     }
   }
?>

But after creating the mysql database, nothing is populated. So my basic question is, Am I doing this right? If not, what am I missing?