Help with Anti Splog plug-in

I’m using the Anti Splog Plug-in by WPMUDEV unfortunately I’m not a member there at the moment. So I’m posting my question here.

the plugin works fine for what i need it for. Now I’m trying to activate the renaming of the wp-signup.php file.
That part works but I’m having a problem with the template. they say.
in the instructions.
Replace any hardcoded links to wp-signup.php with this function: <?php ust_wpsignup_url(); ?> Within post or page content you can insert the [ust_wpsignup_url] shortcode, usually in the href of a link. See the install.txt file for more detailed documentation on this function.

I did and this is what happens
http://bloginsphere.com/http://bloginsphere.com/signup-29f/

this is the html in the theme I’m using original and the replaced

original
<div id="edublog-free"><h3>Get started in seconds for free</h3><p><a href="<?php bloginfo('url'); ?>/<?php if( $bp_existed == 'true' ) { //check if bp existed ?>register/<?php } else { ?>wp-signup.php<?php } ?>" title="Get yourself a free blog">Join Here!</a></p></div>
replaced
<div id="edublog-free"><h3>Get started in seconds for free</h3><p><a href="<?php bloginfo('url'); ?>/<?php if( $bp_existed == 'true' ) { //check if bp existed ?>register/<?php } else { ?><?php ust_wpsignup_url(); ?><?php } ?>" title="Get yourself a free blog">Join Here!</a></p></div>

what can I do to prevent the doubling of the domain. Also BuddyPress is NOT installed.