If you have an .asp site, you should be on a windows server, and if so you should be able to use a web.config file to force all url's over to https. There is an example of the code you want to use in this thread, down a few posts. https://www.ecommercetemplates.com/support/topic.asp?TOPIC_ID=106851
I believe the redirectType="Permanent" part there will throw a 301 response so the SE's will know... You can use an online checker (there are many out there) to check the response of a non https url.