You should be able to move the form fields and form action from the payments page and have it go straight to paypal.
Just move these into the the form on the index page:
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="RPMGY2PMZG4NE">
Then you will have to rename the other form fields to match the paypal naming convention. You can see a reference of the fields available here: https://developer.paypal.com/docs/classic/paypal-payments-standard/integration-guide/Appx_websitestandard_htmlvariables/#auto-fill-paypal-checkout-page-variables