Authorize.Net security issue

I have used the SIM method with [login to view URL] for my payment gateway. After I complete my payment form and view my receipt, I click on a link to return to my site in order to download the video I just purchased and I am experiencing a security warning through the browser telling me, "Although this page is encrypted, the information you have entered is to be sent over an encrypted connection and could easily be read by a third party. Are you sure you want to continue sending this information?" I have purchased the SSL certificate for my site in hopes that it would solve this problem but it did not. I cannot get the link on my receipt page to go to my https version. That being said, I'm not sure what the problem is but I need this fixed so that it is secure and no warnings pop up. I am looking for someone who is very comfortable with these issues to help me fix this.