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The height of the form automatically adjusts depending on the number of form elements that are in that form.
In the URL provided i see that you have added the form twice, with the first one not showing the submit button.
Try enabling the scrolling in your iframe and also increase its height to about 940px
<iframe scrolling="yes" onload="window.parent.scrollTo(0,0)" src="" allowtransparency="true" name="51373906900858" id="51373906900858" style="width: 100%; border: medium none; height: 940px;" frameborder="0"></iframe>