Here is a sample Donation button code you can use:
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_donations">
<input type="hidden" name="business" value="email address">
<input type="hidden" name="item_name" vale="Donation">
<input name="amount" id="amount" type="text" value="" class="form-poshytip" title="USD">
<input type="image" src="https://www.paypal.com/en_US/i/btn/btn_donate_SM.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
</form>
I grabbed the amount
line from your code and added it to mine. I didn't use the "Continue" button on your sample. I put in the actual Donation button image.