Hi,
Try put this in the Styles Property of the iFrame object properties:
border:0;margin:0;padding:0;
and this is my html on server you could try similar (i'm not sure if both are required, but mine autosizes with leadbolt ads and crosswalk):
<!DOCTYPE html><!--HTML5 doctype-->
<html><head>
<head>
<title>Leadbolt Framed Ad for Android Games</title>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
</head>
<body>
<div style="position: fixed; top: 0px; left: 0px; width: 438px; height: 64px;">
<script type="text/javascript" src="http://ad.leadboltads.net/show_app_ad.js?section_id=012345"></script>
</div>
</body>
</html>